I don't know if a similar topic already existed so feel free to do any changes.

This is the rules for the alliance war:

1. This only happens once a month
2. Common and Heroic rarity will be banned in every war
3. There will be specific element boost in each war
4. There will be multiple elements ban in each war
   5 The opponent strength will be determined by alliance point
5. Member must at least have 30 points to qualify for the rewards
6. You must have at least 15 members in order to participate
7. All grade will be increased or lowered to B.

The rewards will be
1.10 gems, 10m food and 7 heroic orbs for number 1-10 or 1-7

2. 5 gems, 4m food and 3 heroic orbs for number 11-20 or 8-15
3. Additional egg reward could be given by social point.

The mechanism:
The war last 2 days, in the prep day you can feed and empower your dragon after battle day you could no longer feed them.
Each member will have 3 attacks, each enemy bases can be attacked up to 3 times and will have 90 points. A player will get 10 contribution points everytime they beat 1 dragon.
The rewards will be given according to your contribution points.
The alliance with the most contribution points win the war.
If you reach certain points, you will be given a mystery egg. It could be common rarity all the way up to VR.

I really think something like this could be implemented. It would add a new dynamic to the game making it even more enjoyable. Some rules could be tweaked here and there, but overall solid idea. I agree something like this should be added.