Guns, manufactured goods, liquor, guns, sugar, medicine, guns, and guns.
One of the common tactics was to pick one ethnic group or whatever to be the "civilized" group, then give them guns and tell them that if they want to continue to get guns they'd better get the rest of the region under control, quick, or the guns would stop. YOu make one group really powerful, but not as powerful as your troops, then use them as a club to beat the rest of the region in to submission while also making your aid contingent on wearing clothes, drinking tea, producing export crops, etc.