Only last week, the government raised its terror alert to high, indicating that a terror attack on Australian soil was "likely".

Today's raids, the largest of their kind in history, mark a new chapter in the fight against terrorism.

Here's how the crisis has unfolded.

01 July 2014 - ISIL declares an Islamic Caliphate that straddles the border of Iraq and Syria. They call it the Islamic state.

19 July 2014 - ISIL claims to have killed up to 270 people in a massacre at the Shaer gas field in Syria. 

28 July 2014 - Australian's Khaled Sharouf and Mohamed Elomar post pictures on Twitter of themselves fighting with ISIL in Iraq. They are holding decapitated heads.

29 July 2014 - AFP issues arrest warrants for Sharouf and Elomar. In 2005 Khaled Sharrouf was sentenced to 5 years jail for conspiracy to commit a terrorist act. Elomar is the nephew of "the puppet master" of a Sydney terrorism cell currently serving time in prison.

9 August 2014 - President Obama authorises targeted air strikes against the Islamic State

11 August 2014 - Sharrouf posts a picture of his 7-year-old son holding a decapitated head on Twitter.

19 August 2014 - ISIL releases footage of US journalist James Foley being beheaded

30 August 2014 - British Prime Minister, David Cameron, raises the UK terror threat to severe. 

1 September 2014 - Foreign minister Julie Bishop says "ISIL is Australia's responsibility" following intelligence that up to 60 Australians could be fighting for the group in Iraq and Syria.

3 September 2014 - ISIL releases footage of US journalist Steven Sotloff being beheaded

10 September 2014 - President Obama launches an open-ended bombing campaign on ISIL strongholds in Iraq

10 September 2014 - A Brisbane book store owner, Omar Succarieh, is arrested in Brisbane on charges of supporting terrorism. He is also the brother of Australia's first suicide bomber, Ahmad Succarieh, who is suspected of detonating himself and a truckload of explosives in north-eastern Syria.

11 September, 2014 - The CIA estimates that there are up to three times the number of people fighting for ISIL as previously thought. "They can muster between 20,000 and 31,500 fighters across Iraq and Syria," a CIA spokesman said.

12 September 2014 - ASIO director David Irvine raises the Australian terror alert to high. 

14 September 2014 - ISIL releases footage of British aid worker David Haines being beheaded

15 September 2014 - Prime Minister Tony Abbott declares war on the "Islamic Death Cult" and announces that 200 special forces troops will be on the ground in Iraq within days, along with 400 air personnel, up to eight FA-18 Super Hornets, and two other aircraft.

18 September 2014 - Australian police launch the largest anti-terror raids in Australian history.