Matthew Arnold, Civilization in the United States: First and Last Impressions of America.

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[16] army entered the city of Mexico. Vera Cruz, Puebla, and other principal cities of the country, were already in their possession. In February 1848 was signed the treaty which gave to the United States Texas with the Rio Grande for its boundary, and the whole territory then included in New Mexico and Upper California. For New Mexico and California, however, the Americans paid a sum of fifteen millions of dollars.

Grant marks with sagacity and justness the causes and effects of the Mexican war. As the North grew in numbers and population, the South required more territory to counterbalance it; to maintain through this wide territory the institution of slavery, it required to have control of the national Government. With great energy and ability, it obtained this control; it acquired Texas and other large regions for slavery; it proceeded to use the powers of Government, in the North as well as in the South, for the purpose of securing and maintaining its hold upon its slaves. But the wider the territory over which slavery was spread, and the more numerous the slaves, the greater became the difficulty of making this hold quite secure, and the stronger grew the irritation of the North to see the powers and laws of the whole nation used