Answer:
The order in which the events occurred is:
1. Saddam Hussein is removed from power.
2. Civil war broke out between ethnic and religious groups.
3. The Islamic States in Iraq and Syria (ISIS) becomes a threat.
4. The United States joins with others to win back Iraqi territories from ISIS.
Step-by-step explanation:
Islamic State is a Sunni Muslim terrorist group struggling to create an Islamic caliphate in the Middle East. Islamic State has grown out of a number of Sunni Muslim rebel groups that emerged after the American invasion to Iraq of 2003.
Prior to the invasion, Iraq was led by Saddam Hussein and the Ba'ath Party, which ironically defeated Islamist groups. After the American invasion of Iraq, al-Qaeda also gained a local branch in the country. After Abu Bakr al-Baghdadi took over the leadership of al-Qaeda in Iraq, there was gradually growing disagreement with al-Qaeda's leader, Ayman al-Zawahiri, who was leading the organization from its hiding place in the Pakistan-Afghanistan border. Among other things, al-Qaeda's leadership thought al-Baghdadi was too violent in its conduct. The disagreements led to al-Qaeda's public withdrawal from its Iraq branch in February 2014, with which all contacts were interrupted.
Then al-Baghdadi chose to change the group's name to "Islamic State in Iraq and the Levant". The movement, which started in Iraq, has grown in recent years in neighboring Syria, fighting both Bashar al-Assad's government forces and Syrian rebel groups, both Islamist and secular. In the summer of 2014, ISIS conquered large parts of Iraq, and on June 29, 2014, Baghdadi declared that the areas controlled by the movement in Iraq and Syria were together a new caliphate. Baghdadi proclaimed himself the new Caliph while changing the name of the movement to Islamic State.
Since 2014, foreign military aircraft and personnel have assisted on various fronts against Islamic State. Russia and Iran have backed Bashar al-Assad and the old Syrian regime and are fighting against both IS and other insurgents in Syria. Since August 8, 2014, the United States has attacked IS from the air in Iraq and since September 22, 2014 also bombed IS in Syria. On October 17, 2017, observers announced that IS had been displaced from Raqqa, which since 2014 had served as a "capital" for IS in Syria.