(CHICAGO) -- Protesters clad in black clashed with police on Sunday at the end of what had been a peaceful march and rally by thousands of demonstrators, led by disenchanted veterans of the Iraq and Afghan wars protesting the opening of the two-day NATO summit in Chicago.
The demonstration was the largest the city has seen in years.
The battle between protesters believed to be members of the anarchist group Black Bloc and police left several demonstrators bloodied, and marred what had been a solemn and orderly march.
At the end of the march, the vets threw their NATO medals over the fence set up by the Secret Service around McCormick Place.
Some of the veterans told ABC News affiliate WLS-TV in Chicago that they had hoped a NATO representative would meet the group and take the medals back as a symbol of recognition.
Former Chicago Police Superintendent Jody Weis criticized the black-clad demonstrators who clashed with police for undermining the emotional power of the veterans' act.
"You have classic Black Bloc ideology, peaceful ceremony, moving ceremony and these individuals use this as an occasion to disrupt, engage the police, engage in criminal activity," Weis told WLS-TV. "Once they crossed that behind and are throwing bribes at the police officers and hitting them with sticks and weapons, then they have no option but to maintain control. It is classic Black Bloc ideology. It ruins ceremonies and ruins a ceremony of veterans turning in their valor medals."
The demonstrators had a wide range of agendas; there were anti-war activists, people concerned about inaction on climate change, and people protesting the handling of the global economy.
But the activists on the street weren't the only ones aiming to disrupt the summit. A hacking group affiliated with Anonymous took responsibility for temporarily crippling the Chicago Police and NATO websites earlier on Sunday.
Chicago police are working with federal authorities to investigate the attack and the extent of it, the Chicago Tribune reported.
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