Tip on the England invasion at the beginning of the game

1.- If you choose to start as William the asshole (for some reason I hate this guy) you have it all easy, wait until the Norway and England armies fight then come in and clean up.

2.- Harold of Godwin, this is the most difficult one in my opinion, you have to retreat your army to wales and hope that before you get a forced surrender the armies of Norway and Normandie meet then just show and clean up.

3.- Harald of Norway, you have to retreat to Scotland until the other 2 guys meet in battlefield and then you show and clean up. The trick here is that you are an old dude and you have to pray to the norse gods you stay alive long enough for Harold and William to destroy themselves then you come in and clean up. Extra tip, if William insta wins by luck (he captures harold) you get an extra dutchy when you win (normandy).

TL;DR whoever you choose to play as, retreat immediately and wait for the other 2 guys to beat the shit out of each other then come clean with your 9k+ army.