Toby B's Mexican American War Timeline By MsOlson Period: Jan 1, 1845 to Dec 31, 1848 Mexican American War Jun 16, 1845 Texas Admitted to the Union Texas accepts the US Congress' offer of annexation and joins the Union. Nov 1, 1845 US Tries to Buy Land Polk sends John Sidell to Mexico with instructions to buy Texas and California from Mexico. Mar 1, 1846 US Troops Stationed at Disputed Border General Taylor's army marched south into the disputed land of Texas. May 1, 1846 US Declares War After a request from President Polk, congress declares war on Mexico Sep 24, 1846 US Victory - Battle of Monterey As part of his plan to cut off Northern Mexico, Taylor's army invades the city and defeats the forces of General Pedro de Ampudia. Sep 14, 1847 Mexico City Surrendered The US army captures and occupies Mexico City. Feb 2, 1848 Treaty of Guadelupe Hidalgo The Treaty of Guadelupe Hidalgo is signed by Mexican Negotiators and it is sent to Washington.