Complex sentence: As LexCorp subsidiaries, the airlines began to prosper and when rising profits were threatened by fuel shortages, LexCorp bought out Southwestern Petroleum, now known as LexOil.
Split into simpler sentences: As LexCorp subsidiaries, the airlines began to prosper. And when rising profits were threatened by fuel shortages, LexCorp bought out Southwestern Petroleum, now known as LexOil.