They will go as far as dropping a nuke that only plants can survive due to the structure of their lungs. They have done this four times before.

There has been one major war. The war lasted 1 hour, and involved them recruiting Luigis, as they were the only mario brother who would actually listen to someone other than peach. A Luigi then became a plant himself, and after this the server began to realize the power of the Plant Army, starting a revolution that would ultimately fail, as the plant army hibernated when they started using plant killer. The general evolved so that he couldn't die to Plant Killer.