I tried two strategies: 1. Kill the ones that seem to move the fastest, hoping it would lead to very peaceful enemies over time. 2. Kill them from left to rig

I tried two strategies: 1. Kill the ones that seem to move the fastest, hoping it would lead to very peaceful enemies over time. 2. Kill them from left to right each round, hoping they would all start gathering at the right hand side of the screen. Neither seemed to do anything special, they seem to just be moving randomly and I get to level 60 or so before I get too bored. I don't understand what it's supposed to do. Am I doing it wrong? :D