You can play the Ho! as a xenophobe, killing everyone you see. Or, if you feel friendly, you can be neutral toward other players (so you don't attack them without cause) or even have a strong alliance (best buddies) in which you share information with your friends. Of course, to form an alliance, both players have to want it.
You show your opinion of the other players by selecting from the popup menu next to each player in the player list in the Map window. A sad face or a happy face will appear next to a player in the player list if the other player thinks differently of you than you do of him.
A standard alliance means that you and your allies' ships don't fight when they are at the same planet. Best buddies go one step more and share all the information they have about the galaxy with their friends.
To break an alliance, just choose a lower menu option in the popup menu. Note: you cannot go from best buddies to enemies in one turn. Once you become enemies, you'll now fight to the death everywhere you coexisted with him. Coincidentally, you'll also earn his permanent hatred and distrust.