The Bart of War

"The Bart of War" is the twenty-first episode of the fourteenth season of "The Simpsons". It first aired on the Fox network in the United States on May 18, 2003. Bart and Milhouse badly damage Ned Flanders' collection of Beatles memorabilia. Under adult supervision, they are then placed in separate youth groups, but the groups go to war.
Plot.
Marge disapproves of Bart and Milhouse watching "South Park", so she unsuccessfully tries to get them to watch "Good Heavens" on PAX. The boys soon find themselves outside the house and bored, and decide to tie a thread to a fly. When the fly enters the Flanders house and is eaten by a cat, Bart and Milhouse find themselves inside the home, unsupervised. They take the opportunity to cause mischief, and discover Ned's collection of Beatles memorabilia in the basement. They drink from cans of a 40-year-old novelty beverage and start to hallucinate, with Bart seeing Milhouse as John Lennon through various stages of his life. When Ned, Rod and Todd return home and discover the damage caused by Bart and Milhouse, they flee to their panic room and call the police. Chief Wiggum and his crew subsequently catch the boys in the basement, and call their parents. They decide that Bart and Milhouse should spend all their time under parental supervision. Bart is also forbidden from playing with Milhouse, who Marge believes incites Bart into his bad behavior.
Marge subsequently establishes a peer group based on Native American life, called the "Pre-Teen Braves" — composed of Bart, Ralph Wiggum, Nelson Muntz, and Database, with herself as tribe leader after Homer fails in his leadership skills. Later, when Marge takes the boys on a nature walk, they meet a Mohican man who shows them a field that is in need of cleaning up. The Pre-Teen Braves agree to the job, but discover that it has already been cleaned by another peer group, the "Cavalry Kids" — led by Milhouse's father, Kirk Van Houten, composed of Milhouse, Martin Prince, Jimbo Jones, and a nerd named Cosine. The two groups try to outdo each other in doing good; for example, when the Cavalry Kids bulldoze the house of the homeless from the Pre-Teen Braves and post a pre-fabricated in place, the Pre-Teen Braves retaliate by setting it on fire with arrows. When the Cavalry Kids sell candy in the hope of becoming batboys at a Springfield Isotopes game, the Pre-Teen Braves try to thwart them by lacing their candy with laxatives. Unfortunately for them, the senior citizens, in need of relief from constipation, buy the Cavalry Kids a win.
At the Isotopes game, in another attempt to defeat the Cavalry Kids, Bart and Homer divert them away from the stadium with a fake "free VIP parking" sign, and the Pre-Teen Braves then disguise themselves as their enemies before singing their own version of "The Star-Spangled Banner". The crowd becomes angered by this, and when the real Cavalry Kids arrive, a fight breaks out between everyone. Marge, appalled by this, starts crying, and when this is shown on the Jumbotron, the fighting stops and the Sea Captain suggests that everyone should sing a sweet, soothing hymn like Canada's national anthem instead of a "hymn to war" like "The Star-Spangled Banner". Everyone present sings "O Canada" to Marge and joins hands to form a maple leaf on the baseball field. Bart and Milhouse then agree that war is not the answer — "except to all of America's problems."