Furious, not a bad idea but it has some serious flaws:
1 - What happens when an ally lose all his bases? reset even when the other ally may be winning the war?
2 - What happens if most of the allies are concentrated into allied country A? Free hunt and base capture at allied country B for the enemy?
3 - What happens when allied country A has no contact with enemy due expansion of alliend country B?
3 side war has demostrated to have serious flaws also. We, at rookland, have been hunted by hordes of knights and bish for weeks. It was common to see 65 bish, 50 knights and 30 or less rooks.
IMO, the key to have an equilibrium is not in the number of countries but in the number of players per country.
For example, triggering a rule when any country has more than 20 players: no one can log into a country that exceeds by 25% or more the number of players of the less populated country.
This way, with a country having 40 players, the other two cant have more than 50 each one. With a rule like this we may have even a successful 2 sided arena.