Mexico had detached itself from Spain in 1826, and in 1833 the province of Texas detached itself from Mexico. Texas was largely peopled by immigrants from the States, and these had grievances. One of them was that Mexico abolished slavery, but there was real misgovernment as well, and, among other cruel incidents of the rebellion which followed, the massacre of rebels at the Alamo stamped itself on American memory. The Republic of Texas began to seek annexation to the United States in 1839, but there was opposition in the States and there were difficulties with Mexico and other Governments. At last in 1845, at the very close of his term of office, President Tyler got the annexation pushed through in defiance of the Whigs who made him President. Mexico broke off diplomatic relations, but peace could no doubt have been preserved if peace had been any object with the new President Polk or with the Southern leaders whose views he represented. They had set their eyes upon a further acquisition, larger even than Texas—California, and the whole of the territories, still belonging to Mexico, to the east of it. It is not contested, and would not have been contested then, that the motive of their policy was the Southern desire to win further soil for cultivation by slaves. But there was no great difficulty in gaining some popularity for their designs in the North. Talk about “our manifest destiny” to reach the Pacific may have been justly described by Parson Wilbur as “half on it ign’ance and t’other half rum,” but it is easy to see how readily it might be taken up, and indeed many Northerners at that moment had a fancy of their own for expansion in the North-West and were not over-well pleased with Polk when, in 1846, he set the final seal upon the settlement with Great Britain of the Oregon frontier.
When he did this Polk had already brought about his own war. The judgment on that war expressed at the time in the first “Biglow Papers” has seldom been questioned since, and there seldom can have been a war so sternly condemned by soldiers—Grant amongst others—who fought in it gallantly. The facts seem to have been just as Lincoln afterwards recited them in Congress. The Rio Grande, which looks a reasonable frontier on a map, was claimed by the United States as the frontier of Texas. The territory occupied by the American settlers of Texas reached admittedly up to and beyond the River Nueces, east of the Rio Grande. But in a sparsely settled country, where water is not abundant, the actual border line, if there be any clear line, between settlement from one side and settlement from the other will not for the convenience of treaty-makers run along a river, but rather for the convenience of the settlers along the water-parting between two rivers. So Mexico claimed both banks of the Rio Grande and Spanish settlers inhabited both sides. Polk ordered General Zachary Taylor, who was allowed no discretion in the matter, to march troops right up