Here is the full list of all 13 War of the Vikings achievements.
Reach rank 60
Reach rank 50
End a game with at least 10 kills and 0 deaths
Win 10 games in a row
Reach rank 40
Kill 10 saxon squad leaders in a single round
Kill an opponent using a throwing dagger
Reach rank 30
Reach rank 20
Kill 10 viking squad leaders in a single round
Reach rank 10
Win one game as the leader of a squad
Revive a squadmate