Complex sentence: In 1972, each league added an eighth team, rebalancing their schedules and resuming their former identities, and they returned to prosperity with the revival of minor league baseball that began in the 1980s.
Split into simpler sentences: In 1972, each league added an eighth team, rebalancing their schedules. They resumed their former, separate identities, and returned to prosperity with the revival of minor league baseball that began in the 1980s.