Both the opening and ending scenes of "The Bart of War" play homage to South Park.
Obviously, the show opens with a spoof of the popular Comedy Central show which, as seen in the spoof often features insane plotlines, over-the-top violence and yes, wacky people in wheelchairs (but no magical farting robots in wheelchairs, sadly) Bart also mentions that the show's only had 43 episodes, a reference to the fact that SP episodes come out very slowly (usually about twelve episodes a year) In real life, the show just passed the hundred-episode mark in the time it took the Simpsons to get to a hundred-sixty.
I'm not sure how they got away with using the show's charecters, name and logo without legal issues, but it might be that the creators of the two shows have some kind of understanding-a South Park episode (titled "The Simpsons Already Did It." ) last year mentioned the Simpsons and various charecters by name several times and even contained a dream sequence where South Park became Springfield and all the SP cast was drawn Groening-style (there was also a cameo by Kent Brockman) So I guess you could say the two shows are even now. ;)
The second reference comes at the end-there was a South Park episode (the Terrance and Philip episode) which also ended with a stadium full of people spontanously breaking into O Canada and a giant maple leaf appearing. It was just as hilariously ironic in that episode,too.
-Wyvern