Complex sentence: The union controlled the market for decades, until the advent of automation in the 1960s meant that machines could make 300 dozen bagels in the time that two men working together could roll 125 dozen.
Split into simpler sentences: The union controlled the market for decades, until the advent of automation in the 1960s. The bagel-making machinery could produce 300 dozen bagels in the time that two men working together could roll 125 dozen.