1848

Migration predated the period of US control notably when Spain sent soldiers and missionaries into the area they named California. It accelerated after the United States seized the Mexican province and immediately profited from the 1848 discovery of gold in the Sierra foothills.

When Mexico won its independence from Spain in 1821, the population of the province of Texas was made of Native Americans and Mexicans. The Mexican government encouraged Americans to settle in Texas to prevent border violations form horse thieves and to protect the territory from Native American attacks.

Like Spain, Mexico also wished to encourage settlement in the state of Coahuila y Texas and passed colonization laws to encourage immigration. Thousands of Americans, primarily from slave states, flocked to Texas and quickly came to outnumber the Tejanos, the Mexican residents of the region.

Texas was annexed by the United States in 1845 and became the 28th state. The annexation of Texas contributed to the coming of the Mexican-American War (1846-1848). The conflict started, in part, over a disagreement about which river was Mexico’s true northern border: the Nueces or the Rio Grande.

In 1845, the Republic of Texas was annexed to the United States of America, becoming the 28th U.S. state. Border disputes between the new state and Mexico, which had never recognized Texas independence and still considered the area a renegade Mexican state, led to the Mexican–American War (1846–1848).

Current Supreme Court precedent, in Texas v. White, holds that the states cannot secede from the union by an act of the state. More recently, Supreme Court Justice Antonin Scalia stated, “If there was any constitutional issue resolved by the Civil War, it is that there is no right to secede.”