Complex sentence: Despite this, Najibullah was not the only choice the Soviets had; a GRU report claimed he was unfit to be leader considering the fact that he was a Pashtun nationalist, a stance which could decrease the regimes popularity even more.
Split into simpler sentences: Despite this, Najibullah was not the only choice the Soviets had. A GRU report argued that he was a Pashtun nationalist, a stance which could decrease the regimes popularity even more.