"Congress doth consent that the...Republic of Texas may be erected into a new state, to be called the State of Texas, with a republican form of government, to be adopted by the people of said Republic."

    In 1835 Texas, aided by private citizens from the United States, rebelled against the government of Mexico. On March 2, 1836 they declared Texas an independent republic. When Mexican President Antonio Lopez de Santa Anna led an army into Texas to put down the rebellion, he was defeated and captured by General Sam Houston at the Battle of San Jacinto, April 21, 1836. While a prisoner, Santa Anna ordered his troops to leave Texas and signed the secret Treaty of Velasco, which recognized both Texian independence and the Rio Grande as the boundary of Texas. Although the Mexican Congress repudiated the treaty, the Republic of Texas maintained its independence. Moreover, an act of the Texian Congress declared the Rio Grande to be the fledgling republic's southwestern boundary, despite the fact that as a Mexican province the border of Texas had been the Rio Nueces, some 160 miles further north. In 1842 the Texians went so far as to send a military expedition, which was unsuccessful, to occupy Santa Fé, New Mexico, a city which lay within the boundary claimed by Texas.

    For nearly ten years the Republic of Texas was an independent country, recognized by the United States, France, Great Britain, and Belgium. Mexico, on the other hand, refused to accept the loss of Texas, considering it to be Mexican territory under the temporary rule of a rebel government. Consequently, when the United States formally offered terms of annexation to Texas in 1845, Mexico recalled her ambassador and threatened war.On July 4, 1845 a Texas convention accepted the U.S. offer, a decision which was overwhelmingly approved by the voters of Texas in the fall. On December 29, 1845, Texas was formally admitted to the Union. In response to Mexico's threats of war, Texas and the United States mutually agreed that the U.S. would station troops on Texas soil as soon as the offer of annexation was accepted. By the end of August 1845, Brigadier General Zachary Taylor (nicknamed "Old Rough and Ready") and his men were in place at Corpus Christi, with more troops arriving almost daily to add to the strength of Taylor's "Army of Occupation."