because the stupid terrorists already have IEDs
What are some mass destruction weapons in Iraq?
There were allegations that Iraq had weapons of mass destruction and considering that Iraq famously used weapons of mass destruction during the Iran-Iraq War, such an allegation was not preposterous.
that Saddam Hussein had weapons of mass destruction.
By claiming Iraq had weapons of mass destruction, making it a threat to national security
There is no definitive answer to this - only theories. There was the claim that Iraq was building weapons of mass destruction. The Bush administration later abandoned that claim, and didn't offer anything in its place.
Weapons of mass destruction
The United States of America, and her allies, blundered into a war in a Iraq, thinking that Saddam Hussein had "weapons of mass destruction" (for example nuclear, biological, chemical weapons), when it fact Iraq did not have "weapons of mass destruction".
None.
The official reason that the president (George Bush) gave was that Iraq had weapons of mass destruction, or nuclear weapons, that were potentially harmful to the USA. The unofficial reason was that America had had enough of Saddam Hussein and wanted him out of government.
The U.S. believed that Iraq possessed weapons of mass destruction
No; they did not think that there was any evidence of 'weapons of mass destruction' inside Iraq; which was the only reason for invading Iraq. As it turned out later, they were right.
There was a belief that Saddam had weapons of mass destruction in Iraq. There was also talk of biological weapons. Terrorists were thought to be hiding out in Iraq and Afghanistan and permitted free operations and perhaps even given aid . Most of this turned out to be untrue.