Protests at Chicago's Nato summit
21 May 2012 Last updated at 16:16 BST
Several thousand protesters marched on Sunday through downtown Chicago to the site of the Nato summit, in one of the city's biggest demonstrations in years.
The activists were demanding an immediate end to the US role in the Afghan war, as well as action on climate change and economic inequality
While the march was largely peaceful, violent clashes broke out between police and demonstrators, as some attempted to march towards the venue where the summit was being held.