At first, the Americans were welcomed into Mexico. The Americans saw Texas as a great opportunity, they wanted to complete Manifest Destiny, good farming and a 'new start'. Mexico favored this because they thought it would increase their economy and make Mexico more stable.
Battle of the Alamo
As the populations of Americans began to increase Mexico began to feel uneasy. Mexico thought that the US was planning to take over Mexico by starting another revolution like the American Revolution.
Santa Anna Forced to Sign Treaty
Santa Anna became President of Mexico but he abused his power. He told the Americans they had to become Mexican citizens, get rid of slaves and convert to Roman Catholic if they wanted to stay in Mexico. This did not go over well with the Americans.
Texas is Annexed into US
The Battle of the Alamo is a very famous battle that took place in the Alamo, an old mission. The Texans decided to stand their ground but were slaughtered by the Mexican troops. The famous battle cry "remember the Alamo" was founded during this battle.
Santa Anna was taken hostage by the Texans and they forced him to sign a treaty declaring Texas as an independent country. Once Santa Anna returned to Mexico he claimed that this treaty was not legal because he had been forced to sign it against his will.
After much debate in Congress, Texas was accepted as an American State. This angered the Northern States as they would not have as much of a say in Congress. It also angered Mexico because Mexico still thought of Texas as its territory.