Do O'Sullivan's and Buchanan's assertions support or undercut the claim that the Mexican War was an aggressive act of imperialism?

Which two statements are true about native american tribes during the civil war? the war caused native american tribes to sign treaties and side with union forces who promised to develop indian territory. the war united the tribes against the confederacy, which wanted to secede from the union and continue slavery. the war created conflicts within the tribes because some wanted to stay loyal to the union, while others wanted to support the confederacy. the war made the tribes forget their differences and come together against the union forces who wanted to abolish slavery in indian territory. the war led native american tribes to sign treaties with the confederacy, which promised to protect the tribes and their interests in exchange for support in the war.