Complex sentence: Mimicking North Korea's Unit 124, which had failed to assassinate President Park in the Blue House Raid, Unit 684 was made up of 31 men, and the Unit's mission was to assassinate the then-leader of North Korea, Kim Il-sung.
Split into simpler sentences: Mimicking North Korea's Unit 124, which had failed to assassinate President Park in the Blue House Raid, Unit 684 was made up of 31 men. Its mission was to assassinate the then-leader of North Korea, Kim Il-sung.