Complex sentence: According to Dreyfuss and Turse, most civilians who died in the conflict did so at the hands of the Taliban and its allies, many thousands of Afghan civilians had been killed by U.S. and allied forces.
Split into simpler sentences: According to Dreyfuss and Turse, most civilians who died in the conflict did so at the hands of the Taliban and its allies. Turse and Dreyfuss found that many thousands of Afghan civilians had been killed by U.S. and allied forces.