What prompted tribes to side with the Confederacy? threats from within the various tribes military victories by the Confederacy complete domination by Union forces promise of additional lands

Answer & Explanation:

The Confederacy took an interest in the territory, seeking a possible source of food in the event of a Union blockade, a connection to western territories, and a buffer between Texas and the Union-held Kansas. At the onset of war, Confederate forces took possession of the U. S. army forts in the area.