Mexico was displeased with the annexation of Texas, but did not manifest so quickly as it was hoped she would and any disposition to avenge herself. Mr. Polk, a Southern man, was now President, and he governed in the interest of the South. A war with Mexico was a thing to be desired, because Mexico must be beaten, and could then be plundered of territory which the slave-owners would appropriate. To provoke Mexico (1846) the unready, an army of 4000 men was sent to the extreme south-western confine of Texas. A Mexican army of 6000 lay near. The Americans, with marvellous audacity, erected a fort within easy range of Matamoras, a city of the Mexicans, and thus the city was in their power. After much hesitation the Mexican army attacked the Americans, and received, as they might well have anticipated, a severe defeat. Thus, without the formality of any declaration, the war was begun.

President Polk hastened to announce to Congress that the Mexicans had "invaded our territory, and shed the blood of our fellow-citizens." Congress voted men and money for the prosecution of the war. Volunteers offered themselves in multitudes. Their brave little army was in peril—far from help, and surrounded by enemies. The people were eager to support the heroes of whose victory they were so proud. And yet opinion was much divided. Many deemed the war unjust and disgraceful. Among these was a young lawyer of Illinois, destined in later years to fill a place in the hearts of his countrymen second only to that of Washington. Abraham Lincoln entered Congress while the war was in progress, and his first speech was in condemnation of the course pursued by the Government.

The war was pushed with vigour at first under the command of General Taylor, who was to become the next President; and finally under General Scott, who as a very young man had fought against the British at Niagara, and as a very old man was Commander-in-Chief of the American Army when the great war between North and South began. Many officers were there whose names became famous in after years. General Lee and General Grant gained here their first experience of war. They were not then known to each other. They met for the first time, twenty years after, in a Virginian cottage, to arrange terms of surrender for the defeated army of the Southern Confederacy!

The Americans resolved to fight their way to the enemy's capital, and there compel such a peace as would be agreeable to themselves. The task was not without difficulty. The Mexican army was greatly more numerous. They had a splendid cavalry force and an efficient artillery. Their commander, Santa Anna, unscrupulous even for a Mexican, was yet a soldier of some ability. The Americans were mainly volunteers who had never seen war till now. The fighting was severe. At Buena-Vista the American army was attacked by a force which outnumbered it in the proportion of five to one. The battle lasted for ten hours, and the invaders were saved from ruin by their superior artillery. The mountain passes were strongly fortified, and General Scott had to convey his army across chasms and ravines which the Mexicans, deeming them impracticable, had neglected to defend. Strong in the consciousness of their superiority to the people they invaded—the same consciousness which supported Cortes and his Spaniards three centuries before—the Americans pressed on. At length they came in sight of Mexico, at the same spot whence Cortes had viewed it. Once (Sept. 14, 1857) more they routed a Mexican army of greatly superior force, and then General Scott marched his little army of 6000 men quietly into the capital. The war was closed, and a treaty of peace was with little delay negotiated.