Sally R. Mexican American War Timeline By MsOlson Period: Jan 1, 1845 to Jan 1, 1849 Mexican American War Jun 16, 1845 Texas Admitted to the Union Texas is admitted to the Union afer much debate. Nov 1, 1845 Us Tried to Buy Land (Sidel and Polk) John Sidel goes to Mexico to try to buy New Mexico and Califonia from them. His mission is leaked and he returns to the States empty handed. Mar 1, 1846 US Troops Stationed at Disputed Border John Sidel is unable to see the Mexican President about buying the land, so the American Troops march to the Rio Grande to hold it. May 1, 1846 US Declares War The United States declares war on Mexico. Congress grants President Polk ten million dollars and fifty thousand volenteers for the war. May 9, 1846 Battle of Resaca de la Palma The American Army wins and drives the Mexican army back over the Rio Grande. Sep 13, 1847 Mexico City Surrenders It takes fourteen hours of fighting and Mexico City surrenders. The American Army captures it and holds it. May 25, 1848 Treaty of Guadelupe Hidalgo The American Congress signed the treaty a couple months earlier, and the Mexican Congress just signed it. The treaty is now put in to place.