In Bemidbar 32:18 the tribes of Gad and Re'uven tell Moshe that they will not return back to their land until all the other tribes have inherited their land portion (after conquering the land and defeating their enemies.)
Moshe proposes in Bemidbar 32:22 that all they needed to do was to help their brothers in battle and defeat their enemies. Once the war was complete, they could return home. They need not wait until they inherited the land.
We see that in actuality, these 2 1/2 tribes waited until everyone inherited their portion before they returned (See Joshua 22) Why did these tribes not accept Moshe's offer?