The tree-like people who march on Isengard in The Lord of the Rings are the Ents.
Ents are ancient shepherds of trees created by Tolkien as the sentient guardians of forests. Their leader, Treebeard, meets Merry and Pippin in Fangorn Forest after the Hobbits escape from the Orcs. The Ents initially hesitate to intervene because they are slow to make decisions, but Treebeard and the other Ents eventually recognize Saruman’s destruction of the forest as a direct threat.
Their march on Isengard is one of the most memorable actions in The Two Towers. The Ents and Huorns overwhelm Saruman’s industrial stronghold, break its defenses, and flood the valley. This attack removes Saruman’s military power even while other battles are taking place elsewhere.
Ents are sometimes confused with Huorns. Both are connected with the trees of Fangorn, but Ents are walking, speaking tree-shepherds with a distinct society. The Eagles are powerful allies in Tolkien’s stories, but they are winged creatures rather than tree-people.