Complex sentence: Land speculators and squatters began to defraud Creeks out of their allotments, and some violence broke out, described by U.S. officials as a so-called "war" by the Creeks that forfeited their prior treaty rights.
Split into simpler sentences: Land speculators and squatters began to defraud Creeks out of their allotments. Some violence broke out, described by U.S. officials as a so-called "war," which they argued forfeited the Creeks' prior treaty rights.