When Congress voted to annex Texas to the United States Mexico's relationship to us turned bad, Mexico took the act as a sign of war. With the U.S. threatening to take Texas a border dispute didn't help men. Mexico and Texas couldn't agree on were the border should be set. Mexico had the border set at the Nueces river and Texas had it at the Rio Grande, giving them more land. James K. Polk, the president, sent General Zachary Taylor and 1,500 troops to guard the Nueces river, but was later sent ward to cross the river, into Mexico. The army marched to Corpus Christi then north, up the Rio Grande. Having been there for a while the Mexicans finally attacked his men. The Mexicans were no match for Taylor and were easily defeated. Taylor saw this as a way to ask congress to declare a war on the Mexicans.
Congress received word that Mexico had shed American blood on American soil (even though it really was on Mexican soil). Having received word of this they took a vote and most voted to declare war on Mexico. This declaration finally took place on May 13, 1846. Mexico's president Mariano Paredes stated, "A greedy people have thrown themselves on our territory...The time has come to fight." Mexico then responded with their own declaration of war on July 7.
General Stephen Kearny led the army of the wets out of Kansas. He was ordered to occupy New Mexico and then continue on to California. Kearny's army was too powerful for the Mexican opposition and the Mexicans realized this, they surrendered without a single drop of blood being spilt. In California a rebellious group led by John C. Fremont tried to take Mexican rule from California. Being large in number the Americans were able to capture and jail General Mariano Guadalupe Vallejo, the Northern California commando. When General Kearny arrived to California with his troops he joined forces with the rebels and they managed to capture all of California.
Meanwhile, General Zachary Taylor was trying to capture Mexico. This was far more difficult then General Zachary had ever thought. First, they had to make their way down through Texas coming from the South. Battling fiercely through Texas he was greeted by an old comrade named General Santa Anna who had marched northward with 20,000 Mexican troops. The two armies fought vigorously to try to defeat each other. Both armies were losing people quickly and in huge numbers so Santa Anna retreated south into Mexico to try to save at least some of his forces.
Thereafter, General Winfield Scott arrived at Veracruz in southern Mexico. They fought hard and steadily through Mexico City, Mexico's Capital. Being so close to the capital the American forces ran into fierce resistance of the Mexican army at the castle of Chapultepec. 1,000 Mexican troops and 100 young military cadets fought bravely to stop the invading forces from capturing the fortress. Their fighting could not withstand the invading forces and Scott's army captured Mexico City on September 1847.
Having fought long and hard, a treaty was finally agreed upon called the Treaty of Guadalupe Hidalgo. In this treaty Mexico agreed to give up Texas and a large area known as the Mexican Cession. It included the present-day states California, Nevada, Utah, Arizona, and New Mexico, also a part of Colorado and Wyoming. This took away half of Mexico's territory but, we agreed to pay Mexico $15,000 and protect the 80,000 to 100,000 Mexicans living in the Mexican Cession and Texas.