In the year 1628, he defended Stralsund, which was besieged by the whole force of the Imperialists, at that time masters of all Germany, that fortress excepted. Here he acquitted himself with the utmost bravery and skill. The plague had already broken out in the city, and the outworks were in a most deplorable condition; yet he compelled count Wallenstein, with a formidable army and flushed with victory, to raise the siege, after having sustained a severe loss. The citizens of Stralsund were so sensible of the services of the field-marshal, on this occasion, that they made him a handsome present, and had medals struck to perpetuate their gratitude and the honour of their deliverer. In the year 1635, he had charters granted to him, his wife, and son, of the barony of Balgonie, and other lands in the counties of Fife, Berwick, and Roxburgh. He was at this time serving in Lower Saxony. In the year 1639, when the covenanters were preparing to resist their sovereign in the field, Leslie returned from Sweden, where he had continued after the death of Gustavus in the service of Christina. "This Leslie," says Spalding, "having conquest from nought wealth and honour, resolved to come home to his native country of Scotland and settle himself beside his chief, the earl of Rothes, as he did indeed, and bought fair lands in Fife; but the earl foreseeing the troubles, whereof himself was one of the principal beginners, took hold of this Leslie, who was both wise and stout, acquainted him with the plot, and had his advice for the furtherance thereof to his power."

It was a fortunate circumstance for the covenanters, that the oppressions to which they had been subjected, and the persecutions that were evidently preparing for them, were well known on the continent, where thousands of their fellow countrymen had been shedding their blood in the defence of the religion and liberties of their fellow protestants, and excited the deepest interest in their favour. Leslie had undoubtedly been invited home, and he brought a number of his countrymen along with him, who, having periled their lives for the same cause among foreigners, could not reasonably be considered as indifferent to its success among their own countrymen. Half a century had, for the first time since it was a nation, passed over Scotland without any thing like general warfare. The people had, in a great measure, become unaccustomed to its hardships and its dangers, and the chieftains, such as had been abroad excepted, were unacquainted with its practice, and ignorant of its details. This defect, by the return of so many who had been in the wars of Gustavus, was amply supplied. Leslie was, by the committee of estates, appointed to the chief command;--many of his fellow adventurers of less celebrity, yet well acquainted with military details and the equipment of an army, were dispersed throughout the country, where they were employed in training the militia, which in those days comprehended every man that was able to bear arms, from the age of sixteen to sixty. By these means, together with a manifesto by the Tables (committees of the four estates assembled at Edinburgh), entitled, "State of the Question, and Reasons for Defensive War," which was circulated so as to meet the eye or the ear of every individual in the nation,—the covenanters were in a state of preparation greatly superior to the king, though he had been meditating hostilities long before he declared them. Though now an old man, little in stature, and deformed in person, Leslie was possessed of ceaseless activity, as well as consummate skill; and in both he was powerfully seconded by the zeal of the people in general. Early apprized of the intentions of Charles, he so managed matters as to render them entirely nugatory. It was the intention of the latter, while he advanced with his main force upon his ancient kingdom by the eastern marches, to enter it previously, or at least simultaneously, on the western side, with a body of Highlanders and Irish, and by the Firth of Forth with a strong division of his English army, under his commissioner the duke of Hamilton. To meet this formidable array, every thing that lay within the compass of their limited means, was prepared by the covenanters. Military Committees were appointed for every county, who were to see to the assembling and training of the militia generally, and to forward to the army such levies and such supplies, as might be from time to time demanded. Smiths were every where put in requisition for the fabrication of muskets, carbines, pole-axes, Lochaber axes, and halberts; magazines to supply the troops were also provided; and to call them together when occasion should require, beacons were provided, and placed in every shire. Arms to the amount of thirty thousand stand were provided from Holland, in addition to those of home manufacture, and a foundry for cannon was established in the Potter Row, at that time one of the suburbs, now a street of Edinburgh. Leith, the part of the capital, was, however, still defenceless; but, aware that the duke of Hamilton proposed to land there with hostile intentions, it was immediately resolved to put the place in a posture of defence. The plan of a new fort, the old defences of the town being in ruins, was laid down by Sir Alexander Hamilton, who acted as engineer to Leslie; and several thousands came spontaneously forward to assist in its erection. Noblemen, gentlemen, and citizens; men, women, and children; even ladies of quality, claimed the privilege of assisting in forwarding the good work, and in less than a week it was finished, and the security of Edinburgh was considered complete. Along the coast of Fife, too, every town was surrounded with batteries mounted with cannon, carried on shore from the ships; and with the exception of Inchkeith and Inchcolm, which were somehow neglected, there was not a resting place in the Firth for an enemy, till he should win it at the point of the pike.

In the mean time, the duke of Hamilton lying in Yarmouth roads, was commanded to sail for the Forth, and by all or any means to "create an awful diversion." His first sail was no sooner discovered as a speck in the distant horizon, than the beacons were in a blaze from the one extremity of the country to the other, and ere he approached the shores of Leith they were lined by upwards of twenty thousand intrepid defenders, among whom was his own mother, mounted on horseback at the head of her vassals, with a pair of pistols in the holsters before her, with which she declared she would shoot her son with her own hand the moment he set a hostile foot on shore. Hamilton now found that he could do nothing. The troops on board his fleet did not exceed five thousand men, all raw young peasants, miserably sea-sick, and many of them labouring under the small pox. Instead of attempting hostile operations, he landed his men upon the islands of Inchkeith and Inchcolm, which served him for hospitals, and contented himself with sending into the town council some more of Charles’s proclamations, which were promised to be laid before the States, who were expected to meet in a few days. This, as the measure of their obedience, Hamilton was for the time obliged to accept. Of this circumstance, with the strength which they mustered, he failed not to acquaint his master, advising him at the same time to negotiate.—We are not detailing the history of the war, but the part performed in it by an individual, or we should have stated that Argyle had been sent to the west, where he had seized upon the castle of Brodick in Arran, where the earl of Antrim was to have first headed his Irish bands, in consequence of which they were for a time unable to come forward. The castle of Dumbarton had also been seized by a master-stroke of policy, as that of Edinburgh now was by the same in war. In the afternoon of the twenty-third of March, Leslie himself, with a few companies which he had been, according to his usual custom, training in the outer court-yard of Holyrood house, some of which he secretly disposed in closes at the head of the Castle Hill, approached to the exterior gate of the castle, where he called a parley with the captain or governor, demanding to be admitted. This being refused, he seemed to retire from the gate, when a petard which he had hung against it, burst and laid it open. The inner gate was instantly assailed with axes, and scaling ladders were applied to the wall, by which the covenanters gained immediate admission; while the garrison, panic-struck with the sudden explosion and the vigour of the attack, surrendered without offering any resistance.

The castles of Dalkeith, Douglas, and Strathaven in Clydesdale, and, in short, all the castles of the kingdom, with the exception of that of Carlaverock, were seized in the same manner. Huntly, who was making dispositions in the north to side with Charles, had also in the interim been kidnapped by Montrose, so that he had actually not the shadow of a party in the whole kingdom. Towards the end of May, the king beginning to move from York, where he had fixed his head-quarters, towards the north, the army under Leslie was ordered southward to meet him. The final muster of the army, previous to the march, took place on the Links of Leith, on the 20th of May, 1639, when from twelve to sixteen thousand men made their appearance, well armed in the German fashion, and commanded by native officers whom they respected as their natural superiors, or by their own countrymen celebrated for their hardihood, and that experience in military affairs which they had acquired abroad. With the exception of one German trumpeter, there was not a foreigner among them: all were Scotsmen, brought immediately from the hearths and the altars which it was the object of the war to defend. The private men were, for the most part, ploughmen from the western counties; stout rustics whose bodies were rendered muscular by healthy exercise, and whose minds were exalted by the purest feelings of patriotism and religion. It was on this day that they were properly constituted an army, by having the articles of war read to them. These had been drawn out by Leslie with the advice of the Tables, after the model of those of Gustavus Adolphus, and a printed copy of them was delivered to every individual soldier. The general himself, at the same time, took an oath to the Estates, acknowledging himself in all things liable both to civil and ecclesiastical censure.

Leslie had by this time acquired not only the respect and confidence, but the love of the whole community, by the judgment with which all his measures were taken, and the zeal he displayed in the cause; a zeal, the sincerity of which was sufficiently attested by the fame of his exploits in Germany, and by the scars which he bore on his person in consequence of these exploits. He was deformed, old, and mean in his appearance; but the consummate skill which he displayed, and the piety of his deportment, rendered him, according to Baillie, who was along with him, a more popular and respected general than Scotland had ever enjoyed in the most warlike and beloved of her kings. With the van of this army, which was but a small part of the military array of Scotland at this time, Leslie marched for the borders on the 21st of May, the main body following him in order. He was abundantly supplied on his march, and at every successive stage found that his numbers were increased, and his stock of provisions becoming more ample. The first night he reached Haddington, the second Dunbar, and the third Dunglass, a strong castle at the east end of Lammermoor, where he halted and threw up some intrenchments.

Charles, in the mean time, advanced to the borders, indulging in the most perfect assurance of driving the Scottish insurgents before him. Learning from his spies, however, that they were within a day’s march of him, and so well marshalled that the result of a contest would be at best doubtful, he ordered a trumpet to be sent with letters from himself to the Scottish army, conveying overtures of a friendly nature, but forbidding them to approach within ten miles of his camp, and on this demonstration of their temporal obedience, promising that all their just supplications should be granted. Finding them disposed to an amicable agreement, Charles advanced his camp to the Birks, on the banks of the Tweed, and directed the earl of Holland, his general of horse, to proceed with thirteen troops of cavalry, three thousand foot, and a number of field-pieces, to drive some regiments of the covenanters which had been stationed at Kelso and Jedburgh under colonel Robert Munro, for the protection of the borders, from their station, as being within the limits stipulated with the noblemen who commanded the main body. Proceeding, in the execution of his order, to Dunse, the first town that lay in his way within the Scottish border, the earl of Holland found it totally deserted of its inhabitants, except a very few, who heard him read a proclamation, declaring the whole Scottish nation, especially all who were in arms and did not immediately lay them down, traitors. Proceeding westward to Kelso, and having reached a height overlooking the town, he found the Scottish troops in the act of being drawn out to receive him. Startled at their appearance, Holland sent forward a trumpeter, to command them to retire according to the promise of their leaders. His messenger was met by a stern demand whose trumpeter he was, and on answering that he was lord Holland’s, was told that it would be well for him to be gone. Displeased with this reception of his missionary, his lordship ordered a retreat, and the Scottish soldiers were with difficulty restrained from pursuing them to their camp.

What share Leslie had in the proposed submission to Charles is not known; but he no sooner heard of the above affair than he broke up his encampment at Dunglass, and set forward to Dunse, where he ordered Munro to join him. Finding here an excellent position commanding both roads to Edinburgh, he formed his camp on the Law behind the town, where he could see the royal camp at Birks, on the other side of the Tweed. This movement was made without the knowledge of the English, whose camp Leslie, had he been left to himself, would most probably have surprised and secured, with all that was in it. Charles himself, walking out after an alarm from the Scottish army, was the first to descry their encampment on Dunse Law, and he rightly estimated their number to be from sixteen to eighteen thousand men; they were soon, however, increased to twenty-four thousand by the reinforcements that hastened up to them on the report of the English incursions at Dunse and Kelso; and never was an army led to the field better appointed, or composed of better materials. "It would have done your heart good," said an eye-witness, "to have cast your eyes athwart our brave and rich hills as oft as I did, with great contentment and joy. Our hill was garnished on the top toward the south and east with our mounted cannon, well near to forty, great and small. Our regiment lay on the sides; the crowners (superior officers of regiments) lay in canvass lodges, large and wide; their captains about them in lesser ones; the soldiers about all in huts of timber, covered with divot or straw. Over every captain’s tent door waved the flag of his company, blue, with the arms of Scotland wrought in gold, with the inscription ‘For Christ’s Crown and Covenant.’ Leslie himself lay in the castle of Dunse, at the bottom of the bill, whence he issued regularly every night, rode round the camp, and saw the watches regularly set." Throughout the whole army there was the most perfect harmony of opinion, both as to matters of civil and ecclesiastical polity; and there was a fervour in the cause they had undertaken, that burned with an equal flame in the bosom of the peasant and the peer. The latter took their full share in all the fatigues of the camp; slept like the common soldiers, in their boots and cloaks on the bare ground; and in their intercourse with their inferiors, used the language of affection and friendship, rather than that of command. Ministers of the gospel attended the camp in great numbers, carrying arms like the rest, and many of them attended by little parties of their friends and dependents. There were sermons morning and evening in various places of the camp, to which the soldiers were called by beat of drum; and while the day was devoted to the practice of military exercises, its rise and its fall were celebrated in every tent with the singing of psalms, reading the Scriptures, and prayer. The general tone of the army was ardent, full of devotion to God and of the hope of success against the enemy. "They felt," says Baillie, "the favour of God shining upon them, and a sweet, meek, humble, yet strong and vehement feeling leading them along. For myself, I never found my mind in better temper than it was all that time since I came from home, for I was as a man who had taken my leave from the world, and was resolved to die in that service without return." While they were thus strengthened in spirit, the body was equally well attended to. The regular pay of the common men was six-pence a day; fourpence purchased a leg of lamb, and all of them were served with wheaten bread; a luxury which it is probable many of them never enjoyed either before or after. Leslie kept open table daily at Dunse castle for the nobility and for strangers, besides a side table for gentlemen waiters; and as there had been an extraordinary crop the preceding year, and the people were zealous to offer supplies, the camp abounded with all the necessaries of life. An amicable arrangement, however, having been entered into between Charles and the covenanters, peace was proclaimed in both camps on the 18th of June, 1639.

In the month of April, 1640, it was found necessary by the covenanters to reassemble their army, and Leslie was again appointed general; but from various causes it was the beginning of August before the general armament could be collected at Dunse, where, in the early part of that month it was reviewed by the general. It amounted to twenty-three thousand foot, three thousand horse, and a train of heavy artillery, besides some light cannon, formed of tin and leather corded round, capable of sustaining twelve discharges each. This was a species of artillery used by Gustavus Adolphus, and which the Scottish general had adopted in imitation of his master. This army was composed of the same men who had last year occupied Dunse Law. The horse were chiefly composed of respectable citizens and country gentlemen, lightly armed; some of them having lances, and generally mounted on the small, but active horses of the country. Their attire and accoutrements were the same as in the preceding year, including the broad Lowland blue bonnet. Their march over the border was, however, delayed for some weeks for the want of money and necessaries. "It was found," says Mr John Livingston, who accompanied the army in the capacity of chaplain to the earl of Cassillis’s regiment, "when the whole army was come up, that there was want of powder and of bread, the biscuit being spoiled, and of cloth to be huts to the soldiers. This produced some fear that the expedition might be delayed for that year. One day when the committee of estates and general officers, and some ministers, were met in the castle of Dunse, and were at prayer and consulting what to do, an officer of the guard comes and knocks rudely at the door of the room where we were, and told there was treachery discovered; for he, going to a big cellar in the bottom of the house, seeking for some other thing, had found a great many barrels of gun-powder, which he apprehended was intended to blow us all up. After search, it was found that the powder had been laid in there the year before, when the army had departed from Dunse Law, and had been forgotten. Therefore, having found powder, the earls of Rothes and Loudon, Mr Alexander Henderson, and Mr Archibald Johnston were sent to Edinburgh, and within a few days brought as much meal and cloth to the soldiers by the gift of well affected people there, as sufficed the whole army. With the same readiness these people had parted with their cloth and their meal, others parted with their plate, and to such an extent was this carried, that for many years afterwards, not even a silver spoon was to be met with in the best houses."—"It was very refreshful," adds Livingston, " to remark that after we came to a quarter at night, there was nothing to be heard almost through the whole army but singing of psalms, prayer, and reading of the Scriptures by the soldiers in their several tents; and I was informed there was much more the year before, when the army lay at Dunse Law. And, indeed, in all our meetings and consultings, both within doors and in the fields, always the nearer the beginning there was so much the more dependence upon God, and more tenderness in worship and walking; but through process of time, we still declined more and more."