Question

What kept Texas from becoming a state until 1845?

Citizens were fearful that it would trigger a war with Mexico.

The Senate tried to override President John Tyler's veto until they finally gained success the fourth time around.

Some members of Congress feared it would tip the balance of power toward the slave states.

The U.S. had to wait for California to gain enough people before entering the Union as a free state.

Answer 1

Some members of Congress feared it would tip the balance of power toward the slave states.

(Annexation was delayed by strong Northern opposition because Texas was a large slaveholding republic — opponents worried it would strengthen the South in Congress. Fears that annexation might also provoke war with Mexico were another important factor.)