Complex sentence: In the early 1980s, with the Soviet Union's international reputation damaged by the invasion of Afghanistan, persecution of dissidents and human rights activists intensified and spelled the end of the groups that were still active at the time.
Split into simpler sentences: In the early 1980s, with the Soviet Union's international reputation damaged by the invasion of Afghanistan, persecution of dissidents and human rights activists intensified. This spelled the end of the groups that were still active at the time.