Original sentence: However, it may often be impossible to reach clear conclusions, since Klan membership was typically secret, and even in cases where known Klansmen were in government, there is no way to prove whether or not a particular action was taken at the behest of the Klan.Some historians, as well as the Klan itself, state that the Klan had vast influence in many state governments, including Tennessee, Indiana, Oklahoma, and Oregon in addition to some of the Southern legislatures
Edited sentence: The Klan claimed vast influence in many state governments, including Tennessee, Indiana, Oklahoma, and Oregon in addition to some of the Southern legislatures