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The slogan “Manifest Destiny” was coined in 1845 by John L. O’Sullivan and referred to the territorial growth the United States experienced in the 1800s. “Manifest Destiny” expressed the conviction that the country’s superior institutions and culture gave America a God-given right, even an obligation, to spread their civilization across the entire continent. 1
While James K. Polk campaigned for the presidency in 1844, he promised the American people that if he was elected he would expand the country. He won the election and became the 11th president of the United States. President James K. Polk 2
In 1845 Congress admitted Texas as a state. This made the Mexican government very angry. They still believed that Texas was a part of Mexico. 3
In September 1845 President Polk sent John Slidell to Mexico City to negotiate the disputed Texas border and purchase New Mexico, California, and Texas for $25 million. Mexico disagreed with the border the U.S. claimed and turned down the money offer. John Slidell 4
In March 1846 President Polk sent General Zachary Taylor and his troops into the disputed territory (land that both the U.S. and Mexico claimed as its own) between the Rio Grande and Nueces Rivers. General Zachary Taylor 5
On April 25, 1846 Mexican troops cross the Rio Grande River and opened fire on U.S. troops at Fort Texas. On May 13, 1846 Congress officially declared war on Mexico. 6
At the start of the war only about 75,000 Mexican citizens lived north of the Rio Grande. As a result, U.S. forces led by Col. Stephen W. Kearny and Commodore Robert F. Stockton were able to conquer those lands with minimal resistance. Colonel Stephen Kearney 7
With the losses adding up, Mexico turned to old standby General Antonio López de Santa Anna, the charismatic strongman who had been living in exile in Cuba. Santa Anna convinced Polk that, if allowed to return to Mexico, he would end the war on terms favorable to the United States. But when he arrived, he immediately double-crossed Polk by taking control of the Mexican army and leading it into battle. At the Battle of Buena Vista in February 1847, Santa Anna suffered heavy casualties and was forced to withdraw. Despite the loss, he assumed the Mexican presidency the following month. General Antonio Lopez de Santa Anna 8
Meanwhile, U.S. troops led by Gen. Winfield Scott landed in Veracruz and took over the city. They then began marching toward Mexico City. The Mexicans resisted at Cerro Gordo and elsewhere, but were defeated each time. In September 1847, General Winfield Scott successfully laid siege to Mexico City’s Chapultepec Castle. During that clash, six military school cadets committed suicide rather than surrender. General Winfield Scott 9
On February 2, 1848, Mexican and U.S. officials signed the Treaty of Guadalupe Hidalgo officially ending the War. This treaty gave the United States California, Nevada, Utah, most of Arizona, and parts of New Mexico, Colorado, and Wyoming. 10