Maybe make EXP useful? EXP is just to level up, but I think it would be a good idea to make something out of leveling up, for example:
level 5: A random I Item for all Members
Level 10: A PERK HAS BEEN ADDED
Level 15: A random II Item for all members
Level 20: A random III Item for all members
Level 30: A random IV Item for all members
Level 40: A random V Item for all members
Level 50: A PERK HAS BEEN ADDED
Level 60: A random VI Item for all members
Level:70: A random VII Item for all members
Level 80: A random VIII Item for all members
Level 90: A random Elite Item for all members
Level 100: A random Elite Item for all members and A NEW PERK HAS BEEN ADDED
also what life said about leveling up is easy... maybe it can be made so it is a bit hard?
Maybe Clan Event Squad could be a thing, squad that makes clan events (like what Dextile68 mentioned) or Event Squad could do it or just automatic events/tournament (like what Erth mentioned).

The idea of the level up and get something out of it maybe could make everyone be interested in those events? @Life


People could make alts to get items for themselves but like I said maybe it could be hard?
what I mean by hard is lower the amount of EXP that people get by mass-warring and higher the amount of exp you need to level up everytime you are on a new level.