Complex sentence: He ran this modest business successfully and during the early Allied occupation of Berlin also became involved in the making of peanut butter destined for American troops, this sideline became so successful that he considered exiting painting.
Split into simpler sentences: He ran this modest business successfully, and during the early Allied occupation of Berlin also became involved in the making of peanut butter destined for American troops. This sideline became so successful that he considered exiting painting.