The Nagorno-Karabakh conflict between Armenia and Azerbaijan, explained

An ethnic Armenian soldier stands guard next to Nagorno-Karabakh's flag atop a hill in the separatist region in Azerbaijan in November 2020. (Sergei Grits/AP)

The conflict between Armenia and Azerbaijan over the contested Nagorno-Karabakh region has simmered for decades. In 2020, the two sides fought a bloody war for territory — one that ended with a fragile Russian-brokered truce.

But on Monday night, fierce clashes erupted again near the disputed region, which is inside Azerbaijan but controlled by ethnic Armenian separatists.

Azerbaijan and Armenia exchange fire in Nagorno-Karabakh border zone

Armenian officials said at least 49 people were killed in attacks by Azerbaijan’s military. Azerbaijan acknowledged launching the strikes — but said it was responding to Armenian provocations.

The renewed fighting prompted the State Department to call for an immediate end to the hostilities. Reuters reported Tuesday morning that Secretary of State Antony Blinken spoke overnight with both the Armenian prime minister and president of Azerbaijan.

Russia is a key ally of Armenia, and some observers speculated that Azerbaijan may have sought to attack while Moscow is bogged down by a tough fight in Ukraine.

Here’s what you need to know about the fight over Nagorno-Karabakh, the longest-running conflict in the post-Soviet sphere.