Troops trained at your military academy and stationed in your town. Their combined defense points protect you from attackers.
Soldiers of yours that survived a country war and now hold the territory. They cannot be recalled and they do not defend your own town, but they fight on the defending side if that land is attacked again before their term runs out.
Troops need housing just like citizens — build enough houses or your army has nowhere to live.
Every force you have marched on a foreign town — those still on the way and those that have already fought. Open any battle to see exactly what happened.