Obviously, at some point, the High Druids decided that all this probably wasn't so good for the bits of landscape playing host to the battles. After some petitioning, and possibly a few battles of their own, involving magically animated trees, they managed to get most of the sides involved to agree to only start wars over "proper" things, like territory, farmland, kidnapped royalty, and suchlike, rather than any time a king felt the national ego could do with a boost.
For times like that, there is now Grudgeball.
Grudgeball is usually played on a large oval or square field. Two teams of of players try to hit the ball (actually a goblin skull alchemically treated to give it bounce) through the opposing team's goal hoop using hefty wooden mallets. A Druid referees, and makes a vain attempt to enforce the "no intentionally hitting other players with your mallet" rule. The ball may be handled with the mallet, or the head or body of a player, but not the feet or hands.
A Grudgeball team is made up of 11 players, 8 of whom may be on the field at any one time. Up to two of these players may be "heavies" (defined as anything that's more than 10 feet tall when it stands up straight, or that weighs more than 25 stone), with the special limitation that if both heavies are deployed on the field at once, if one is incapacitated or sent off, their "slot" must be left open, and not filled with a normal player from the bench.
Arcane magic is usually banned on the field, but divine magic is permitted (on the grounds that nobody is willing to tell a god he's not allowed to get involved), although smiting of players is generally considered bad form. Intentionally enchanted mallets and other items are likewise banned, although some relic mallets that have picked up a sort of ambient enchantment from the belief of the fans do see use (and get stolen a lot by rival teams), and golems and reanimated dead are permitted (on the condition that they can say "I am a player" to the Druid referee).
Games usually last an hour, or until a riot breaks out.