WASHINGTON — UKRAINE isn’t the only place where Russia is stirring up trouble. Since the Soviet Union broke up in 1991, Moscow has routinely supported secessionists in bordering states, to coerce those states into accepting its dictates. Its latest such effort is unfolding in the South Caucasus.

In recent weeks, Moscow seems to have been aggravating a longstanding conflict between Armenia and Azerbaijan while playing peacemaking overlord to both. In the first week of August, as many as 40 Armenian and Azerbaijani soldiers were reported killed in heavy fighting near their border, just before a summit meeting convened by Russia’s president, Vladimir V. Putin.

The South Caucasus may seem remote, but the region borders Russia, Iran and Turkey, and commands a vital pipeline route for oil and natural gas to flow from Central Asia to Europe without passing through Russia. Western officials cannot afford to let another part of the region be digested by Moscow — as they did when Russia separated South Ossetia and Abkhazia from Georgia, just to the north, in a brief war in 2008, and when it seized Crimea from Ukraine this year.

Conflict between Armenia and Azerbaijan is not new. From 1992 to 1994, war raged over which former Soviet republic would control the autonomous area of Nagorno-Karabakh, a mountainous region with a large Christian Armenian population of about 90,000 within the borders of largely Muslim Azerbaijan. The conflict has often been framed as “ethnic,” but Moscow has fed the antagonisms. That war ended with an Armenian military force, highly integrated with Russia’s military, in charge of the zone. The war had killed 30,000 people and made another million refugees.