Complex sentence: The allotment regime created by the Dawes Act was never intended to be a permanent fixture; it was supposed to transition gradually into fee simple ownership over a period of 25 years, about one generation.
Split into simpler sentences: The allotment regime created by the Dawes Act was never intended to be a permanent fixture. The expectation was that Native Americans would gradually assume fee simple ownership of lands over a period of 25 years, about one generation.