Complex sentence: The Westerner remnants, led by Yi Gwi, saw Gwanghaegun's recent loss of support from the scholars as a chance for the Westerners to regain power, and decided to stage a coup to bring down Gwanghaegun.
Split into simpler sentences: The Westerner remnants, led by Yi Gwi, saw Gwanghaegun's lack of support from the scholars as a chance for the Westerners to regain power. Yi decided to stage a coup to bring down Gwanghaegun.