Opponents with a similar score (kills and trophies) will fight against each other, this means that your Alliance will be matched against Alliances with a similar amount of trophies.

As your Alliance begins to climb the rankings by gaining more and more trophies, the trophy difference may become bigger and bigger. Some of the reasons for this may be caused by the following:

• Fewer Alliances further up the ladder don't have as many trophies as your Alliance, so the server widens the trophy pool to search for another Alliance.
• Some Alliances around your Alliance trophy count may not be participating in the next Alliance War.