In The Two Towers, the second volume of Tolkien's The Lord of the Rings, the Ents — usually very patient, deliberate beings — do become angry at Saruman, whose armies are cutting down (in their eyes, killing) large numbers of their trees. They convene an Entmoot, a meeting of the Ents of Fangorn Forest at Derndingle to discuss the argument of going to war.
After a lengthy deliberation of three days (though from the perspective of the Ents, this was a very quick debate), they come to the conclusion (in the book) to destroy Isengard, and head toward it. They are led by Treebeard, the oldest Ent, and accompanied by the hobbits Meriadoc Brandybuck and Peregrin Took. They destroy Isengard in an all-out assault and trap Saruman in the tower of Orthanc.
