Complex sentence: He marketed his idea, and by 1938, he was supplying the mud to all American League teams; because Blackburne was a die-hard American League fan, he refused to sell the mud to National League teams until the mid- 1950s.
Split into simpler sentences: He marketed his idea, and by 1938, he was supplying the mud to all American League teams. Because Blackburne was a die-hard American League fan, he refused to sell the mud to National League teams until the mid- 1950s.