Complex sentence: Just after World War II, the market share for the Coca-Cola Company's flagship beverage was 60%, and in 1983 it had shrunk to under 24% in the face of competition from Pepsi-Cola.
Split into simpler sentences: Just after World War II, the market share for the Coca-Cola Company's flagship beverage was 60%. By 1983 it had declined to under 24% because of competition from Pepsi-Cola.