Many American settlers were upset and disliked the idea of taking orders. They had been so used to self-government that this change was too much for the them. They also had no desire to become Mexican citizens. All official documents were also done in Spanish. Most Americans knew little to no Spanish.
Tejanos hated how the Americans kept coming illegally. They also disliked the lack of respect these Americans had for Mexican culture and truly disliked how they were refusing to become citizens.