The war is waged by space ships, troop transports, and planetary defenses. All battles happen sequentially in random order at the start of each turn, see Initiating Battles.
Combat phases
-
A space battle, either a Tactical Combat or a Strategic Combat. This stage determines which military ships are destroyed or retreat. It is possible to destroy a colony during this phase if enough damage has been dealt to the planet.
-
A Planetary Bombardment. If the defender has no fleets or defensive structures left, the attacker may bomb the colony randomly destroying during this phase. Each bomb may randomly destroy a military unit, a building or a unit of population. Depending on your goals you may want to do maximum damage to the colony or to damage it just enough to successfully capture it on step 3.
-
If you have a stellar converter in a fleet you can destroy a planet instead. There is no defense from it, the colony is destroyed in one shot and the planet becomes an asteroid belt.
-
-
A Ground Combat. You need to have transport ship(s) in your fleet for this. It plays automatically, you capture the colony if successful.
-
A telepathic takeover is an alternative way to capture a colony. Possible for telepathic races if large enough ship is present. This can be thwarted if defending side is telepathic or has a leader with a telepathic skill deployed in a system.
-