For the first time in six years, the North Atlantic Treaty Organization announced that it would expand its membership, inviting Montenegro to join the alliance. Only 16 years ago, NATO was bombing the small western Balkan nation as part of its intervention in Kosovo.

With a standing military of only 2,000, Montenegro’s membership will have little impact on the alliance’s military strength. But the move has profound political consequences. It illustrates the progress that the western Balkans, and Montenegro in particular, have made since the bloody and traumatizing wars of the 1990s. To receive the invitation, Montenegro had to undertake a series of political, legal, and military reforms under the auspices of NATO’s Membership Action Plan, a program that offers assistance and support for countries seeking to join the alliance.

That a newly independent country could reach these standards in such a short time frame speaks to the enduring and powerful draw of the Euro-Atlantic community. In that sense, this remarkable success story comes at an opportune time—it is a bright spot in Europe’s otherwise dark political terrain of internal strain, the refugee crisis, and the war in Ukraine.

Protesters flee from tear gas in the center of Kosovo's capital Pristina, November 18, 2015. Police and protesters clashed in Kosovo for a second day on Wednesday in a deepening crisis over relations with former ruler Serbia. Hazir Reka / Reuters

Montenegro’s membership also represents a major step toward consolidating political stability and democracy in the western Balkans; the reforms it undertook to reach this point include strengthening its governing structures and democratic institutions, as well as bringing its military up to NATO standards. NATO membership would also turn Montenegro into a regional leader and an example of how a small country, not even a decade old, can make great strides so long as it has enough political ambition. The move could inspire others, such as Macedonia and Bosnia and Herzegovina, to reenergize necessary reforms for eventual membership, a process that has stagnated in both countries. Montenegro’s invitation would also send a signal to Georgia and Ukraine that NATO is, in fact, honoring its “open door policy,” which was questioned in the face of Russia’s annexation of Crimea.

Russia is staunchly opposed to NATO expansion due to its deep-seated and historical fear of being “encircled” by a potential adversary. Within Russia, President Vladimir Putin inflates the threat of NATO as the country’s top geopolitical foe in order to stoke Cold War–era tensions and consolidate domestic power. This makes curbing NATO expansion a strategic priority for Russia. Unsurprisingly, Russia quickly denounced NATO’s invitation to Montenegro, which gained independence from Russia’s natural ally in the region, Serbia, only nine years ago. Russia’s Foreign Ministry called the decision “an openly confrontational step fraught with additional destabilizing consequences for the system of Euro-Atlantic security” and Dmitry Peskov, President Vladimir Putin’s spokesman, said that NATO’s expansion “cannot but result in retaliatory actions … from the Russian side.”

Such warnings are likely rhetorical. Montenegro is more geographically insulated from Russia than Georgia or Ukraine. It’s more likely that Russia will retaliate through political or economic channels instead. Already, pro-Russian groups in Montenegro have taken to the streets to protest against NATO membership and have also called for the resignation of Montenegrin Prime Minister Milo Djukanovic. Russia may stoke further civil unrest in order to make the country appear too unstable to join NATO. That may not be difficult to do. Domestically, Montenegro faces anti-NATO factions including from within both the Orthodox Church and political parties that emphasize ties to Serbia and Russia over NATO.

Russia also has substantial economic leverage over the country, particularly in the tourism and real estate industries (an estimated 40 percent of Montenegrin real estate is Russian-owned); thus, Moscow, which placed a food embargo on Montenegro after it sided with the West on Ukraine, could slap on more sanctions in order to further punish the country for its Western-leaning political ambitions.

Kosovo Serb boys stand on the street during a protest, October 17, 2011. Marko Djurica / Reuters

Domestically, Montenegro’s public is skeptical that NATO membership will be economically beneficial and is wary of the current government’s motives, since Djukanovic, the very man who has steered his country toward NATO inclusion, has been charged with financial corruption. An investigation by the BBC in 2012 found that he and his associates were using a partially public-funded bank for their own personal use.

When the 28 NATO members vote on Montenegro’s membership in the coming year, Russia can fund anti-NATO political parties in countries more susceptible to Russian money, such as Hungary, Greece, or the Czech Republic, to vote, “no.” In the past, NATO members’ parliaments have always deferred to their government’s decision on NATO enlargement, but since the decision requires unanimous consensus among all 28 members, Russian influence remains a risk.

The most likely scenario, however, is that Russia will look to prevent Serbia from following Montenegro’s path. In recent years, Russia has worked to consolidate influence in Serbia and Republika Srpska, the ethnically Serb entity in Bosnia and Herzegovina, through economic aid and military cooperation.

The EU opened accession talks with Serbia in the wake of the announcement about Montenegro’s NATO membership. This demonstrated a rare example of coordination between NATO and the EU, two institutions that struggle to work together because of political divisions between two of its members, Turkey and Cyprus. But this move also opens new avenues for Russia to derail progress in the Balkans, either through Serbia’s EU accession talks or through the fragile Serbia-Kosovo peace deal that the EU brokered in 2013.

Crises in the Middle East and Ukraine have pushed the Balkans down on the priority list for many transatlantic leaders. But it is time to pay attention to the region again. Its relative calm and peace should not be taken for granted. Economic distress and the refugee and migrant crisis have stretched the Balkans’ fledgling democracies to their limits and opened new avenues for Russian interference. Bosnia risks backsliding into political turmoil, and Macedonia’s ambitious political and democratic reforms suffered a monumental setback this summer after a scandal over the government’s wiretaps of opposition leaders and ethnic violence in the Kumanovo region. Even the watershed Serbia-Kosovo peace deal hangs by a thread today; Kosovo erupted in protests last month after the government made a deal with Serbia to integrate Serb-majority regions in Kosovo—a move supported by Brussels. These are manifestations of deep-seated and unresolved political, ethnic, and economic stresses that are bubbling beneath the surface of ostensible progress toward European integration. That is why Montenegro’s NATO membership invitation, although a major milestone, does not mean that peace in the region is a foregone conclusion.