What did the british do when they came overseas to america and encountered the native american indians?
What did cortez and the other spaniards do when they came to mexico and encoutnered the native aztecs?
What did whites do when they went to africa and found black people?
Every situation where a superior group has encountered an inferior group - the inferiors are either enslaved or wiped out.
I try to be optimistic that aliens, due to their level of advancement, will be more friendly and peaceful, but if they're anything like humans they will view us as slaves and nothing more.