The 2003 invasion of Iraq, from March 20 to May 1, 2003, was spearheaded by the United States, backed by British forces and smaller contingents from Australia, Spain, Poland and Denmark. Four countries participated with troops during the initial invasion phase, which lasted from March 20 to May 1. These were the United States (248,000), United Kingdom (45,000), Australia (2,000), and Poland (194). 36 other countries were involved in its aftermath. The invasion marked the beginning of the current Iraq War. In preparation for the invasion, 100,000 U.S. troops were assembled in Kuwait by February 18. The United States supplied the vast majority of the invading forces, but also received support from Kurdish troops in northern Iraq.
According to the President of the United States of that time; George W. Bush and the Prime Minister of the United Kingdom of that time; Tony Blair, the reasons for the invasion were "to disarm Iraq of weapons of mass destruction (WMD), to end Saddam Hussein's support for terrorism, and to free the Iraqi people." According to Blair, the trigger was Iraq's failure to take a "final opportunity" to disarm itself of nuclear, chemical, and biological weapons that U.S. and coalition officials called an immediate and intolerable threat to world peace. Although some remnants of pre-1991 production were found after the end of the war, U.S. government spokespeople confirmed that these were not the weapons for which the U.S. went to war. In 2005, the Central Intelligence Agency released a report saying that no weapons of mass destruction had been found in Iraq.
In a January 2003 CBS poll 64% of U.S. nationals had approved of military action against Iraq, however 63% wanted President Bush to find a diplomatic solution rather than going to war, and 62% believed the threat of terrorism would increase in the event of war. The invasion of Iraq was strongly opposed by some traditional U.S. allies, including France, Germany, Chile, New Zealand, and Canada. Their leaders argued that there was no evidence of WMD and that invading Iraq was not justified in the context of UNMOVIC's February 12, 2003 report. On February 15, 2003, a month before the invasion, there were many worldwide protests against the Iraq war, including a rally of 3 million people in Rome, which is listed in the Guinness Book of Records as the largest ever anti-war rally. According to the French academic Dominique Reynié, between January 3 and April 12, 2003, 36 million people across the globe took part in almost 3,000 protests against the Iraq war.