Complex sentence: Considerable evidence exists that the Soviet Union knew about the US-Pakistan support for the Mujahideen, and the KGB might have seen this as an opportunity to punish both Pakistan and the United States.
Split into simpler sentences: Considerable evidence exists that the Soviet Union knew about the US-Pakistan support for the Mujahideen. The KGB might have seen this as an opportunity to punish both Pakistan and the United States.