Actually we didn't. The Texas territory was opened to white and Mexican settlers by the Mexican government. They allowed the Texans to settle if they converted to the catholic faith. They started over taxing these settlers and there was a revolt. The Mexican government sent Santa Anna up to stop it. Santa Anna was defeated and Mexico, in the surrender, ceded the lands to the Texans. They were not invaded or occupied. Learn history and you won't get schooled on these threads.