Galvanized by the American attack on Iraq, anti-war activists set off a barrage of street protests around the world, clashing with riot police, chaining themselves together, blocking traffic, walking out of classes and parading in mock chemical suits.
Hundreds were arrested from San Francisco to Washington, DC on Thursday.
There were counter demonstrators, too. One in Mississippi carried a sign saying, "Support the US Or keep your mouth shut."
"This is no ordinary day," said Jason Mark, a San Francisco activist. "America is different today: We've just launched an unprovoked, unjust war."
Hundreds of thousands of protesters marched on American embassies in European capitals and in Manila, the Philippines.
In Egypt, riot police used water cannons and attack dogs to keep anti-war demonstrators away from the US Embassy. Protesters hurled stones, pounded cars and shouted against the United States and Egypt's leaders.
"We want the flag down. We don't want America here at all," said a 21-year-old demonstrator who identified himself only as Seoudi, 21.
Police at one point unleashed four or five police dogs, scattering panicked protesters.
Police reports said some 37 protesters and police were injured.
In Buenos Aires, Argentina, federal policemen fired tear gas grenades and rubber bullets to scatter demonstrators who stoned the US Embassy, burned an American flag and chanted slogans describing US President George W Bush as "a fascist terrorist." No damage was reported to the Embassy.
Hundreds of Ecuadorans marched on the US Embassy in the capital Quito, burning US flags and chanting "Bush is an assassin."
Ecuador's vice president, Alfredo Palacio, described the start of war on Iraq a step backward for humanity.
Italians marched by the thousands in Rome and other cities, and the country's powerful trade unions organised two-hour work strikes.
Police in Rome stopped demonstrators from reaching the US Embassy. In Milan, some marchers faced off with police at the US Consulate. In Trieste, authorities scuffled with protesters tr ying to enter a building where a US Consular agent works.
In Athens, Greece, more than 100,000 people marched to the US Embassy, where their rally ended peacefully. But violence brok e out in the northern Greek city of Thessaloniki, where demonstrators set fire to a car and hurled eggs and red paint at police.