Fighters from the Fajr Libya (Libya Dawn) militia sit on pick up trucks mounted with a machine gun during clashes with forces loyal to Libya's internationally recognised government near the Wetia military air base, as they fight for control of the area some 170 kilometres west of the capital Tripoli on January 5, 2015. (Mahmud Turkia/AFP/Getty Images)

WHEN LIBYA’S attempt to construct a new, democratic political system faltered after 2012, the Obama administration and NATO allies who had intervened to support the overthrow of dictator Moammar Gaddafi could still rationalize that they had headed off the mass bloodshed and civil war that the Gaddafi regime threatened and that later overtook Syria. The respite, however, proved to be temporary. As 2015 begins, Libya is well on its way to becoming the Middle East’s second war zone — with the same side effects of empowering radical jihadists and destabilizing neighboring countries.

The sprawling but sparsely populated country of 7 million is now split between two governments, parliaments and armies, one based in the eastern city of Tobruk and the other in the capital, Tripoli. While Syria’s war is fought along the Arab world’s Sunni-Shiite divide, in Libya the contest pits the region’s secular Sunnis against Islamists (along with minority Berbers). Since that same divide dominates the politics of Egypt, Tunisia, the Palestinian territories and much of the rest of the Maghreb, outside powers have predictably picked sides: Egypt and the United Arab Emirates back the secular forces in the east, while Turkey, Qatar and Sudan support the Islamist Libya Dawn in the west.

This mounting conflict is occurring not so much because of NATO’s 2011 intervention, which was limited to airstrikes, but because of its swift withdrawal and subsequent failure to assist in stabilizing the country. Without institutions or trained and loyal security forces, an interim government could not gain control over the numerous militias that had sprung up to fight the Gaddafi regime. As the situation has steadily worsened in the past two years, the Obama administration, France, Britain and other participants in the NATO intervention have reacted not by dispatching aid but by shutting down their embassies and washing their hands of Libya. The task of trying to broker peace has been handed to a U.N. mediator, Bernardino León, who in recent interviews has described his mission as quixotic.

As in Syria, this passivity could soon produce a serious threat to Western interests. According to the U.S. Africa Command, 200 jihadists linked to the Islamic State already have set up a training camp in the eastern Libyan town of Derna. Only 300 miles from southern Europe, Libya could — far more easily than Yemen or western Iraq — become the launching pad for more attacks on Paris and other Western capitals.

The only sign that the Obama administration is conscious of this threat has been the issuance with its allies of empty statements, such as one Saturday that congratulated Mr. León for scheduling talks in Geneva this week among some of the warring parties. Real progress toward ending the fighting would require more energetic action, such as diverting Libya’s oil revenues to an escrow account, enforcing an arms embargo, freezing the international assets of both sides and pressuring Egypt and other outside powers to cease their interventions. Ultimately, an international peacekeeping force probably will be needed to help restore order.

The Obama administration is, as always, reluctant to mount or even support such an effort. Yet doing so now is surely preferable to being forced, as in Iraq and Syria, to conduct another military intervention in the future.