The Tripods Trilogy by John Christopher

In a dystopian future where Earth is controlled by giant, three-legged machines known as Tripods, humanity has been subjugated through the use of mind-controlling caps. The story follows a young boy named Will and his friends as they embark on a perilous journey to join a group of rebels who are determined to overthrow the Tripods and reclaim human freedom. As they navigate through various challenges and uncover the secrets of the Tripods' origins, the protagonists must confront their fears and make difficult choices to ignite a revolution against their alien oppressors.