Numbers 31 - 32

Moses was instructed to go to battle against the Midianites, and that after the battle he would come to the end of his life.  The kings of Midian were defeated, as well as Balaam the prophet who had brought trouble upon them by his pronouncements to king Balak.  The spoils of war were carefully considered, so that no further contamination would be brought into the population.  Several of the tribes petitioned Moses to have their inheritance on the eastern side of the Jordan.  Moses granted their request on the condition that they would not fully receive their land until they had assisted their fellow countrymen in the battles to conquer the western side of the river.