Why were the northerners against annexing Texas?

1. Fear of disrupting the balance of power between slave and free states: The admission of Texas, a vast expanse of land south of the Missouri Compromise line, would upset the delicate political balance between free and slave states, potentially granting Southern slaveholders a disproportionate influence in the Senate and electoral college.

2. Concerns over expansionism and the spread of slavery: Many Northerners opposed the expansion of the U.S. territory, especially if it meant extending the institution of slavery. The annexation of Texas was seen as a potential gateway to future territorial acquisitions in the Southwest, leading to the perpetuation and possible expansion of slavery.

3. Diplomatic complications with Mexico: Texas' independence was still unrecognized by Mexico, which regarded its annexation by the U.S. as an act of aggression. Northerners worried that annexing Texas could lead to war with Mexico and further territorial disputes.

4. Economic protectionism: Some Northerners believed that the inclusion of Texas could adversely affect their economic interests. By adding new agricultural territories to the Union, they feared competition from Southern cotton and wheat production, potentially depressing Northern economic industries.

5. Political and geographical divisions: Some Northern states viewed the annexation of Texas as a move driven by the South to enlarge its political power and dominance. There was resistance to territorial expansion that catered primarily to Southern demands, and some saw it as a challenge to the equilibrium among different regions of the country.