According to Pitchfork, the front man of Arcade fire, Win Butler had a cameo appearance in the National's opening act at UCI Pavilion in Chicago last night. When the band started performing a song called " Start a war", Butler jumped on the stage and started singing a chorus with them. Thanks to the internet, we are able to see this dream collaboration. I just wish there was a high quality video out somewhere. Let me know if you find a good one. This is the best one that I've discovered. The chatting in the background bugs me a bit while trying to concentrate on their performance. Yet, it is still epic to encounter a performance with such talented singers.