Northern lawmakers were hesitant to go to war with mexico because they feared  a.  the southern land gained from mexico would end up as free states.      b.  that spain would reconquer a weakened mexico.      c.  the strength of the mexican army.      d.  the southern land gained from mexico would end up as slave states.

The correct answer should be A. the southern land gained from Mexico would end up as free states.   

This would mean that these new states would now as slave states help the south become more powerful in the congress and the northern idea of ending slavery would be jeopardized. This includes territories like Texas, Nevada, California, Arizona, and similar.