History of Isengard
It was built in the second age along Orthanc by the Númenoreans in the Second Age, during the establishment of the realms of Gondor and Arnor.
Saruman attempted to claim Isengard after returning west from his travels. He wanted to defend the west, and he was welcomed by King Frealaf and Steward Beren. However, he later showed his true colors in Lord of the Rings, when Gandalf arrived and saw its transformation and Saruman was gathering an army.
The Battle of Isengard occurred in March 2nd with its attack beginning by the Ents of Fangorn. They overtook the orcs and men, but were unable to assail the tower. A few days later, Merry and Pippin welcomed the others, including Théoden, Éomer, and Gandalf. Saruman refused to cooperate with them despite their efforts to do so.