2 opponents on the same planet

[ExChairman (OP)]

I am in the process off moving troops to a planet where I have two hostile races. When I land, will they both attack as one or as two separated attacks? Do I attack both or only one? Newer had this tactical exercise before... 

[Erik L]

I believe you determine which one to attack. Of course, I could be wrong.

[Garfunkel]

When your troops land, they create a colony. You can go into the Colony View, click on Ground Units tab and then from a pull-down menu select who to attack. You cannot attack both at the same time, though each 5 days you can change the target. If you do not have out-power the enemy, do not attack as you'll just be wasting your forces. On the defensive they can whittle the enemy strength away while you ship in more troops.

[MarcAFK]

If you can create an additional colony on the planet that would allow splitting the forces up.