Why did America start the war with Iraq?

the governments of the United States and the United Kingdom claimed that Iraq's alleged possession of weapons of mass destruction posed a threat to their security and that of their coalition/regional allies : a combined force of troops from the United States, the United Kingdom, Australia, and Poland, invaded Iraq and deposed the Ba'athist government of Saddam Hussein : The invasion phase consisted primarily of a conventionally-fought war which concluded with the capture of the Iraqi capital of Baghdad by American forces.