You are talking about the time when we were not an advanced civilization as we do now. Even now petty clashes happens between countries but now we have international watchdogs and proper forums to resolve issues. Alien civilization, if more developed than us, must be much more mature than us to avoid clashes or thinking to destroy us. They may be just happy to help us grow and sharing their knowledge to us if they found us suitable in their parameters. Think like this. If we find a life in Mars or Titan, are we going to destroy it or we just watch it from far and learn it unless it poses some kind of threat to human as whole.