ISIS fighters train at a camp in Benghazi, Libya, in May 2015. Media Office Wilayat Barqa/Islamic State group

The northern Libyan city of Sirte is home to some of the country's largest oil drilling operations and a major seaport, and has a history of housing Libya’s most brutal players. It was both the birthplace and the site of the death of Libyan dictator Moammar Gadhafi, who was killed during the 2011 Arab Spring protests. Four years later, it has fallen into the hands of the Islamic State group. On Thursday, militants seized an airport that houses the base that NATO forces bombed to oust Gadhafi.

The airport was previously under the control of militias loyal to the Tripoli-based General National Congress, one of two governments and several militias currently fighting for control of the country. Forces loyal to the GNC, which is not recognized by the international community, were forced to retreat from the airport and nearby military base, making it one of the most significant military gains yet for the group also known as ISIS branch in Libya.

"After they left, Islamic State group fighters entered the base, which had been completely emptied of equipment except for one military plane, which is out of use," Mohamad al-Shami, an GNC spokesman, told Agence France-Presse.

Earlier this year, the head of the United Nations Support Mission in Libya, Bernardino León, said the country was “very close to total chaos.” With the growth of ISIS in the country, Libya’s civil war has now become more complicated and chaotic than ever.

The GNC and Libya Dawn, a coalition of militias who vary from the secular tribesman from Misrata to more radical Islamist fighters, control the capital and have been fighting forces loyal to ISIS on the ground in Tripoli and Sirte.

The GNC is also fighting the rival government located at the other end of the country in Tobruk, the internationally recognized House of Representatives and military forces in Operation Dignity, an armed group led by former Libyan general Khalifa Hifter. They too are battling their opposing faction and the ISIS insurgency.

The militant group entered Sirte in February and as of last week controlled the majority of the city, which lies between Tripoli and Benghazi.

ISIS has been active in Libya for several months and has declared three wilayats, or states, within the country, where it has opened media, military, training and recruitment operations. The three states are likely connected under one leader and coordinate their operations within the country, according to a report from the Institute for the Study of War.

Libya has been in the throes of a civil war since Gadhafi was ousted in 2011, leaving behind an abundance of weapons and dozens of extremist groups. Among those still active are Ansar al-Sharia in Libya, a militant group formerly aligned with al Qaeda with ties to a Tunisian group with the same name. The Shura Council of the Youth of Islam, a militant group active in Derna, was the first group in Libya to pledge allegiance to ISIS.

“Libya wilayats are gaining strength primarily by convincing local groups to align with ISIS ideologically and adopt ISIS’ style of warfare,” according to ISW. “ISIS is likely to continue operations in Libya as long as other militant actors are focused on the country’s ongoing civil war."