How do I get fiefdoms?

You don’t get them by yourself. Your Alliance is able to earn them by fighting war seasons. So first join a team and make sure the team has at least 8 active members, that’s a precondition for participating in the war seasons.

Do your raids on the war map on wars going on with your team to help them win wars. Every war you win when you attack gives you an extra fiefdom. When other alliances attack fiefdoms your team is defending, make sure to win those, otherwhise you lose fiefdoms. When you win the most fiefdoms on the map, or make as much an other team and score the most skulls, you are rewarded with war boosts like doom gate, frenzy blaster or surprise mummy just to name a few. The war boosts you get depend on the season. team that becomes first gets three war boosts, number two 2, number three 1 war boost.

The more fiefdoms your team has, the stronger the war boosts is one of the advantages. A disadvantage can be that you face stronger opponents. You will figure out very fast how it all works.