Causes of the Mexican-American War Initially, the United States declined to incorporate it into the union, largely because northern political interests were against the addition of a new slave state. The Mexican government was also encouraging border raids and warning that any attempt at annexation would lead to war.

The war officially ended with the February 2, 1848, signing in Mexico of the Treaty of Guadalupe Hidalgo. In return, the United States paid Mexico $15 million and agreed to settle all claims of U.S. citizens against Mexico.

The Treaty of Guadalupe Hidalgo was a peace treaty signed on the 2nd of Feburary, 1848, at the Villa de Guadalupe Hidalgo (presently known as Gustavo A. Madero, D.f). The signing of this treaty ended the war between the United States and Mexico.

As a result of the war, the United States acquired Puerto Rico, Guam, and the Philippines as territories.

How did the Spanish try to avoid war with the United States? Spain freed cuba and turned over the islands of Guam in the Pacific and Puerto Rico in the West Indies to the United States. Spain also sold the Philippines to the United States for 20 million.

On April 21, 1898, the United States declared war against Spain. The reasons for war were many, but there were two immediate ones: America’s support the ongoing struggle by Cubans and Filipinos against Spanish rule, and the mysterious explosion of the battleship U.S.S. Maine in Havana Harbor.

U.S. victory in the war produced a peace treaty that compelled the Spanish to relinquish claims on Cuba, and to cede sovereignty over Guam, Puerto Rico, and the Philippines to the United States. The United States also annexed the independent state of Hawaii during the conflict.