...The country is coming undone. Relentless factional fighting in Tripoli and in the eastern city of Benghazi has left dozens of people dead. Well-known political activists have been killed, diplomats have been kidnapped, and ordinary citizens fear bandits on the roads.

Water and electricity shutdowns have become more frequent than at any time since the chaos after Colonel Qaddafi’s fall, and fuel has disappeared from Tripoli’s gas stations. On Sunday, several Western nations advised their citizens to leave immediately. Gunmen attacked a convoy of British diplomats....

This time, the fighting in Tripoli seems at least partly fueled by the campaign of a general named Khalifa Hifter, who vowed in May to rid the country of Islamist militias. He and his self-proclaimed national army have focused their fight in Benghazi, where daily battles with the militias have settled into a deadly stalemate.

Mr. Hifter has won support from Libyans who fear the growing assertiveness of extremists, especially in eastern Libya. But his campaign has also stirred new divisions, and violence, across the country. Militias from the coastal city of Misurata that oppose Mr. Hifter have been clashing for weeks around the Tripoli airport with fighters from the mountain city of Zintan, who support him....