In 1998 , a wealthy dissident Saudi Islamist , Osama bin Laden , declared a fatwa calling for the killing of " Americans and their allies -- civilians and military ... in any country in which it is possible to do it " in order to bring to an end the ongoing enforcement of the sanctions against Iraq and presence of US troops in the Arabian Peninsula , thus bringing Australians into the line of fire in what would latterly grow to be defined as the War on Terror . Following the 11 September terrorist attacks by Al-Qaeda in 2001 , On 14 September 2001 , the Australian Government cited the terrorist attacks against the US as sufficient basis for invoking the mutual-defence clauses of the ANZUS Treaty . This was the first time the Treaty 's clauses on acting to meet a common danger had been invoked since it was enacted in 1952
11 September terrorist attacks
September 11 attacks
History of Australia since 1945