Yay, the first combat is in the game! This is just the basics of ground combat, not everything is implemented yet. However everything required for conquering planets are implemented.
The missing features are:
Ability to capture units in combat - If you win the battle, those captured units become a part of your population. This is a good way of obtaining that research race that you want to fill your research planets with.
Ability to capture technologies in combat - If you've captured some units, there's some chance that you may capture some of their technologies. If no units are captured, you won't be able to capture anything.
Technology bonuses - Better technologies give you an edge in battles. Right now, all races are equal in ground combat.
Before you look at the ground combat screenshot, please pardon my crappy background art. You can see that humans has invaded a planet owned by a race of Zero People, and that humans are losing the battle. Here's the screenshot!