The Fairly OddParents S03E04 - Love Struck

Having been rejected by Trixie on Valentine's Day, Timmy wishes that the population be divided by gender, thus Dimmsdale (and, to a greater extent, the world) splits into Hersdale (Female's world) and Himsdale (Male's World) by a wall. Unfortunately, because no love is spreading, Cupid is nearing his death. Timmy is the only one who knows what is missing, and cries because nothing fills the void. Timmy destroys the wall, causing the genders to come in contact with each other, but instead of falling in love like Timmy planned, they go to war against each other. Timmy falls in love with Tootie, instead of Trixie, at the end of the episode.