Police, protesters clash as thousands rally against NATO in Chicago (PHOTOS)

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Anti-NATO protesters at a rally before a march toward McCormick Place in Chicago, where world leaders are attending a NATO summit.
- [Meena Thiruvengadam/GlobalPost]
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Police prepare for the beginning of a march from Chicago's Grant Park toward McCormick Place, where world leaders were holding their 25th summit. The Chicago police department was out in force with hundreds of officers lining up down the march route and and dozens buses filled with riot police standing by.
- [Meena Thiruvengadam/GlobalPost]
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The march started calmly with some of the thousands of protesters in attendance even running into old friends among Chicago's police force.
- [Meena Thiruvengadam/GlobalPost]
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Veterans in Chicago prepare to march against NATO ahead of throwing their war medals across a fence behind which world leaders were meeting.
- [Meena Thiruvengadam/GlobalPost]
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Veterans in Chicago prepare to march against NATO ahead of throwing their war medals across a fence behind which world leaders were meeting.
- [Meena Thiruvengadam/GlobalPost]
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Anti-NATO protesters march from Chicago's Grant Park toward McCormick Place, a convention center where world leaders were holding their 25th NATO summit.
- [Meena Thiruvengadam/GlobalPost]
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Anti-NATO protesters formed a "black bloc," dressing in black clothing and face masks as they walked through the steamy streets of downtown Chicago.
- [Meena Thiruvengadam/GlobalPost]
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Anti-NATO protesters begin a march from Chicago's Grant Park toward McCormick Place, a convention center where world leaders were holding their 25th NATO summit.
- [Meena Thiruvengadam/GlobalPost]
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Anti-NATO protests brought together several groups protesting on behalf of or against various causes.
- [Meena Thiruvengadam/GlobalPost]
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Photographers and anti-NATO protesters seek out higher ground.
- [Meena Thiruvengadam/GlobalPost]
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Demonstrators clash with police officers as they protest during the first day of the North Atlantic Treaty Organization (NATO) Summit May 20, 2012 in Chicago, Illinois.
- [Joshua Lott/Getty Images]
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Protesters and Chicago Police confront each other near the NATO conference venue on the first day of the NATO summit on May 20, 2012 in Chicago, Illinois.
- [Spencer Platt/Getty Images]

CHICAGO — Thousands of protesters marched against a variety of causes, including the war in Afghanistan on Sunday as Afghanistan dominated a meeting of sixty heads of state at the 25th NATO summit. Sunday's largest protest started peacefully in Grant Park but ended with protestors facing off against riot police a few blocks from McCormick Place, where leaders were meeting. Several people have been arrested so far, and there have been at least a handful of reported injuries.