Complex sentence: In the 2015 CUPE 3903 strike at York University, leading IS members played a divisive role, refusing to work with existing networks, and unsuccessfully attempting to block what ended up being a victorious strike.
Split into simpler sentences: In the 2015 CUPE 3903 strike at York University, some say leading IS members played a divisive role. They allege that the I.S. members refused to work with existing networks, and unsuccessfully attempted to block what ended up being a victorious strike.