The United Nations is a real-life organization that is aimed to keep peace and security between different nations and was established after World War II to prevent any future wars from occurring. It has appeared several times throughout South Park, first appearing in the film South Park: Bigger, Longer & Uncut.
In South Park: Bigger, Longer & Uncut, the United Nations is seen when the Canadian Ambassador gives an angry speech after the American military has reprehended Terrance and Phillip. He tries to make a point to the American delegates, but is simply laughed at due to his pronunciation of "about".
In "A Ladder to Heaven", George W. Bush talks to the United Nations about Saddam Hussein creating weapons of mass destruction in Heaven. Bush tells them about Saddam's relationship with Satan, prompting one of the ambassadors to ask him if he's high or incredibly stupid.
In "Canada on Strike", Stephen Abootman demands more money from the United Nations after nobody takes Canada Appreciation Day seriously. The United Nations refuses and Stephen and the rest of Canada goes on strike until they get what they want. At the end of the episode, the United Nations agree to give the Canadians coupons to Bennigan's and free bubblegum, but to act like they're giving them a lot.