Texas, after revolting and winning independence from Mexico, chose to join the US after a short jaunt as an independent nation.

The rest, yea, pretty much forcefully taken in one way or another.

Seems like this was the Mexican's mistake: "In the hopes that an influx of settlers could control the Indian raids, the bankrupt Mexican government liberalized immigration policies for the region. Finally able to settle legally in Texas, Anglos from the United States soon vastly outnumbered the Tejanos. Most of the immigrants came from the southern United States. Many were slave owners, and most brought with them significant prejudices against other races, attitudes often applied to the Tejanos. Mexico's official religion was Roman Catholicism, yet the majority of the immigrants were Protestants who distrusted Catholics"