ISIS's hold on parts of Iraq and Syria was brutal, especially for Iraq's Yazidi population.
It group's reign of terror began in 2014, and at one point it spanned one-third of both countries.
The group was renowned for its extreme violence and cruelty, but after years of intense fighting, it has now been defeated.
In March, the US-backed Syrian Defense Forces (SDF) said ISIS fighters had been defeated in the last piece of territory they had held in the east of the country.
In a post on Twitter at the time, the head of the SDF media office declared the "total elimination of (the) so-called caliphate."
Some of those who perhaps suffered more than most were the Yazidi people - one of Iraq's religious minorities. Thousands were slaughtered, and women and girls were forced into sex slavery.
Journalist Norma Costello traveled to Dohuk in northern Iraq for RTÉ News and spoke to victims.
Viyan was sold 22 times by ISIS, with the abuse so bad that she tried to end her life by drinking chemicals. She said Yazidi men were killed and then fed to dogs. Viyan also thinks those responsible should be subject to the same torture she received.
Kni is aged in her 50s. The beatings she received resulted in her losing all her teeth. Her period with ISIS lasted seven months and she says what they did will never be forgotten.
Styfan is 14 years old, and when he was taken by ISIS, he was separated from his family and forced to work digging tunnels. Styfan was beaten and told he was a slave.
Another young woman said she was raped many times and nearly lost her sight after being hit so often. She wants justice to be served.
Angus Lambkin, an Irishman, witnessed firsthand the suffering of the Yazidi people and others in Mosul, Iraq.
The city was the scene of intense fighting between ISIS and Iraqi forces, and Lambkin arrived in 2017 as part of the United Nations Irish Aid Rapid Response Corps.
Speaking to RTÉ News, he said there is no doubt Yazidi people were subjected to terrible abuse, adding that prior to the battle, it was clear they were enslaved by ISIS. "They suffered enormously," he said.
It is clear that the ISIS regime is over but has left behind countless victims.