The protagonist in "The Destructors" is the Wormsley Common Gang; their objective in the story is to completely raze the magnificent house owned by Mr. Thomas to the ground, leaving nothing behind. The reader could interpret the story as having multiple antagonists.
Society: First, the antagonist could be society in general, because one of the primary conflicts in the story is man versus society. The Wormsley Common gang wants to destroy the old house, because they are rebelling against the image it projects of upperclass society.
The House: The house itself could be viewed as an antagonist, because the boys work against the fixtures and structure in their collaborative attempt to destroy it.
Mr. Thomas: Mr. Thomas is the most obvious choice as antagonist, because the boys attempt to circumvent his authority by destroying his house and locking him in the outhouse.
The story is set among the ruins created by German bombing during World War II. These children whom the author calls "the Destructors" have grown up during the bombing raids, and their reaction to the destruction has been somewhat different from that of the adults. The children thought that the explosions and fires were glorious and exciting. The deaths were things that happened to other people. If they had been older they would have been able to cause greater destruction with bullets and bombs, but they have missed a golden opportunity. They have come to love destruction. In normal times they would have grown up to be normal boys, but in abnormal times they have grown up to be little savages. The real protagonist and antagonist in this war story are Britain and Germany. Germany might be considered the protagonist because we only see the destruction wrought by their bombing planes as well as their V1 and V2 rockets. That would make Britain the antagonist. Even though the war is over, the conflict lingers on in the children. It will take perhaps a hundred years for all the aftereffects of such a great war to be resolved and forgotten. It might be said that this terrible destruction of a priceless house is just another minor event in the war, something like an aftershock following an earthquake. The war is over, but there are still countless wounded to be cared for, orphans to be housed and educated, ruins to be torn down and trucked away, new buildings to be constructed on the ravaged sites. And there are millions of veterans and civilians all over Europe and even in America who have been so badly psychologically injured that they will never recover completely. The situation portrayed in Graham Greene's story is duplicated by inference in Germany, Austria, the Soviet Union, Italy, and elsewhere. In some parts of Europe many children are even worse off than those in "The Destructors." Small orphaned children on the continent are living on their own among the ruins and scavenging for food. "The Destructors" only depicts an incident in an all-out war between nations.