On February 15, 2003, two and a half million Italians marched past the Coliseum protesting the impending war in Iraq. The banners they waved and the death masks some of them wore symbolized their outrage at American aggression and indifference to international law. But they were also protesting against their own government's support for the war and in favor of a host of domestic claims, ranging from pension reform to unemployment to the legal problems of Prime Minister Berlusconi (della Porta and Diani 2004).

Those Romans were not alone. On the same day in Paris, 250,000 people marched against the war; in Berlin, half a million walked past the Brandenburg gate; in Madrid, there were a million marchers, in Barcelona 1.3 million; in London, 1.75 million people – the largest demonstration in the city's history – spread out across Hyde Park to protest against the war and Prime Minister Blair's support for it. Even in New York, in the face of rough post-9/11 treatment from the NYPD, more than 500,000 people assembled on the east side of Manhattan.

On that day in February, starting from New Zealand and Australia and following the sun around the world, an estimated 16 million people marched, demonstrated, sang songs of peace, and occasionally – despite the strenuous efforts of organizers – clashed with police. This was probably the largest international demonstration in history.