Complex sentence: However, their journey to Ba Sing Se is complicated when Appa is kidnapped and, managing to reach the city, find the Earth King Kuei and the Ba Sing Se manipulated by Long Feng, the leader of the Dai Li secret police.
Split into simpler sentences: However, their journey to Ba Sing Se is complicated when Appa is kidnapped. They learn that the Earth King Kuei, along with everyone in Ba Sing Se, are manipulated by Long Feng, the leader of the Dai Li secret police.