The Mifflin Street Block Party has become a right of passage for many students at the University of Wisconsin in Madison. Think what you may of it, it's a persistent event and has proceeded annually on the first Saturday in May since the 1960's. Although attempts have been made by the city and business interests to co-opt it, it will continue to take place with or without sanction.
The party had its origins in the sixties as an anti-war protest against the school's complicity with the military-industrial complex -- particularly in regard to the Dow Chemical corporation which was recruiting students to make napalm and agent orange. Additionally, the event became a dance party in the streets to show solidarity with the rebellion in France in '68. Police responded violently to the party, as is their wont, and the students fought back. This is undoubtedly part of the reason why Madison earned the reputation as being the "Berkeley of the midwest."
As the party continued to manifest annually, thanks to the rebellious spirit of youthful students, it continued to have political messages tied with it. For example, in 1984, a commemorative t-shirt design was opposed to U.S. involvement with Nicaragua. And, of course, this was fitting for an event such as this one in a progressive city such as Madison.
However, over the years, the authorities have attempted to co-opt the party. The city has given tenuous approval (of an event it couldn't stop) and businesses have been allowed to set up stages and push corporate booze. It might even be argued that the city and the university has encouraged drunkenness and apolitical revelry at this event. This is effectively what has happened (by design or not).