Complex sentence: Before allotment, reservation territory was not owned in the usual western sense, but was reserved for the benefit of entire Indian tribes, with its benefits apportioned to tribe members according to tribal law and custom.
Split into simpler sentences: Before allotment, reservation territory was not owned in the usual European-American sense, but was reserved for the benefit of entire Indian tribes. The communal benefits were apportioned to tribe members according to tribal law and custom.