The Fastest way to get this is by starting a Ranked Online match. It is dead so you will need a boosting partner to get this done!!!
The person NOT going for the achievement build up an army and send them into the middle of the match. Have your command (Person needing the achievement) run out into the crowd and snape back to your homebase nod and stay at the menu where you purchase more throops. When your commander is dead, this achievement will unlock