The humans versus the buggers. This is the central conflict in Ender’s Game. As to why it exists:
“‘Why are we fighting the buggers?’
This exchange compels me to consider our own intra-species conflict. How many disputes are down to our inability or unwillingness to communicate, to our lack of empathy and forgetfulness? How many fights are caused because masters don’t remember what it is to be an apprentice? What damage is brought about by the old forgetting what it is to be young, the haves forgetting what it is to be a have-not, and the cynical forgetting what it feels like to have hope?
Put more succinctly: are all the ills of the world caused by fragmented communication, by a deteriorated empathic ability and our unwillingness to imagine ourselves in any role other than the one we currently occupy?