Complex sentence: During a 20-year riding career, John Rotz won many of the most important races across the United States, and in 1969 and 1970, he won more stakes races than any other jockey in American racing.
Split into simpler sentences: During a 20-year riding career, Rotz won many of the most important races across the United States. In 1969 and 1970, he won more stakes races than any other jockey in American racing.