Furor Teutonicus Achievement
Defeat all opponents instead of collecting the required Relics in the first Barbarossa mission.During the first Barbarossa mission your mission is to collect the Relics, instead ignore them completely, do not touch the relics at all. Instead build a large army and go out to kill every enemy. Obviously best to do this on easy difficulty.
Bohemia can actually become a hard enemy but has no army at the start so you will want to attack them immediately. They are located in the northeast and can be defeated using your starting army. It is also relatively easy to defend your island you start on as there are only four ways to it.