Complex sentence: After Zero Hour, the future of the DC Universe was completely rebooted and instead of an established Legion, a new Legion with younger heroes was just beginning, and the history between the 21st and 30th centuries had changed.
Split into simpler sentences: After Zero Hour, the future of the DC Universe was completely rebooted. Instead of an established Legion, a new Legion with younger heroes had just been formed, and the history between the 21st and 30th centuries had changed.