Why was the annexation of Texas opposed by many Americans?

The North opposed slavery while the South believed it was alright. Annexing Texas would increase the number of slave states, thus enhancing slave power. Adopting Texas into the Union would also mean war with Mexico. Texas was land Mexico was hoping to get back.

The North opposed slavery while the South believed it was alright. Annexing Texas would increase the number of slave states, thus enhancing slave power. Adopting Texas into the Union would also mean war with Mexico. Texas was land Mexico was hoping to get back.