Which simpson episode has that box war when ...
What happens in Springfield stays in Springfield!
season 18 ep 15 – Rome-old and Juli-eh
” Bart and Lisa order a lot of complimentary shipping boxes from the A.S.S. (American Shipping Services, not affiliated with the human ass), getting the idea from Ned Flanders, and build a fort out of them. When the Sarcastic Man becomes angry and asks for them back, they refuse, whereupon he threatens to come back and get them by force. Bart and Lisa think he is bluffing, but in fact he comes back with an army of delivery men and women. Bart and Lisa put up a brave fight, first by releasing a barrage of cardboard tubes to trip the enemies, then using cardboard squares to throw like shuriken. The delivery men and women set up a siege ladder and Lisa wraps the lead man in tape and pushes the ladder down. They are aided by Nelson, who arrives unexpectedly to aid Lisa, who could have been hit by a barrage of cardboard arrows. He dives down with twin cardboard tubes and fends off a large number of delivery men and women, while one of the enemies flies overhead, upon a giant, red Fell Beast.
The army swarms while Bart uses a cardboard tube to shoot down enemies with bricks, beehives, egg cartons and Snowball II. The A.S.S. legion fails and flees, but the kids immediately lose interest in their fort and melt it with the garden hose (ignoring the dead Fell beast nearby).”