Tom Clancy's EndWar

This will be one of the last multiplayer trophies you earn, to get this you must fully kill 500 enemy units while in Theatre of War matches. As is mentioned in other spots in the guide, to "fully" kill an enemy unit you must order your units to attack again after an enemy unit has been downed. If they are Evacuated by the rescue Helicopter, the kill will not count. This will take quite a while, but the fastest way is for you to deploy transports and engineers and for your boosting partner to deploy Gunships and send them to you. If there is Raid mission type open on a given day as the attacking faction, a much faster method is to destroy the drones that are stationed by each critical building. Each drone counts as a kill. As you are boosting other trophies you will naturally pick up a bunch of kills, so it may be best to wait on this towards the end unless Raid is available. You can verify how many kills you earned in a match on the results screen.

If you're going for this legit, you will still want to play Raid missions when they are available in Theatre of War. Other than that there's nothing else you can do but just continue to play. This will be difficult because legit players online routinely engage in unit-killing to keep opponents' units at a lower level. The trophy will pop when you have killed your 500th unit.