More than 100 people have been killed in southern Syria since Sunday, according to a war monitoring group, in one of the deadliest bouts of sectarian violence in the region in years.

The clashes erupted on Sunday between Bedouin groups and militias drawn from the Druse religious minority that control the southern province of Sweida. Those clashes set off days of fighting in a rugged stretch of southern Syria, throwing a spotlight on the difficulties Syria’s new government has had asserting its authority over the country.

The conflict has also drawn in neighboring Israel, which launched a wave of airstrikes at Syrian government forces in Sweida. On Tuesday, government reinforcements entered the province, and the Syrian minister of defense announced a cease-fire. Here’s what you need to know:

Why did the fighting erupt?

The fighting started on Sunday after members of a Bedouin tribe attacked and robbed a Druse man along Sweida’s main highway, according to the Syrian Observatory for Human Rights, a war monitor based in Britain. That incident prompted an exchange of attacks and kidnappings between Druse militias in Sweida and armed Bedouin groups there, some of which are seen as pro-government.

As that unrest swelled, the Syrian government deployed military forces on Monday to quell the conflict, Syrian officials said. But given the deep-seated mistrust of the new government, many in the Druse militia groups thought that the government forces were coming to aid the Bedouins and attack the Druse, according to Druse militia leaders.

In response, many of the Druse militias mobilized to repel the government forces and clashed with them, Druse militia leaders said. Israel also intervened, carrying out a wave of airstrikes on Monday and Tuesday against Syrian government troops in Sweida.