Complex sentence: In 1968, while at Damascus University, Kazak was invited to join the Palestine National Liberation Movement (Fateh) which was at the time underground and which is now the largest party within the PLO.
Split into simpler sentences: In 1968, while at Damascus University, Kazak was invited to join the Palestine National Liberation Movement (Fateh). At the time the movement was underground, it is now the largest party within the PLO.