[Tomgs]

To use ground combat you have to be in the same sector as the planet. Either use tactical combat or make sure you have the right strategy selected for your ships in Strategic combat. I don't use strategic combat often so I don't know the name of that strategy. You have to make sure that if there are defences on the planet or ships in orbit that you can defeat them also because you have to be adjacent to the planet with your troop transports to start ground combat.