In 1999, NATO was dropping bombs on Montenegro, a small state in southeastern Europe that at that point was part of the Federal Republic of Yugoslavia alongside Serbia. Sixteen years later, things have certainly changed. If a now-independent Montenegro gets what it hopes for, it could be asked to join NATO in just a few months.

“I am certain the conditions are there for the alliance member states in December to take the decision to invite Montenegro to join,” Montenegrin Foreign Minister Igor Luksic told Reuters.

Top NATO officials have been visiting Montenegro this week, a trip they say is designed to assess whether the country has made progress on reforms required to join the alliance. The country is one of four seeking NATO membership (alongside Bosnia-Herzegovina, Macedonia and Georgia), but experts say it is most likely to join next.

For the alliance, Montenegro's ascension to NATO wouldn't exactly prove a game changer. The country has a population of not much over 600,000 and a military budget of $28 million – a paltry figure when compared with, say, Britain, where $55 billion has been spent on defense over the past year. The Montenegrin armed forces number around 2,000 during peacetime, and one recent government report suggested that they were desperately in need of modernization.

However, despite Montenegro's small size, many in Europe will be watching the situation closely for one big reason: Russia.

Russian President Vladimir Putin has complained for years about NATO's eastern expansion, often arguing that the alliance broke promises made at the end of the Cold War. "I think it is obvious that NATO expansion does not have any relation with the modernization of the alliance itself or with ensuring security in Europe," Putin said in a scathing speech at the 2007 Munich Security Conference. "On the contrary, it represents a serious provocation that reduces the level of mutual trust."

European concerns about Russia's reaction appear to have ended talk of NATO membership for Georgia, a former Soviet republic on Russia's southern border that fought a brief war with its larger neighbor in 2008. Putin has also suggested that Russia's intervention in Crimea was a result of concerns about NATO. "I simply cannot imagine that we would travel to Sevastopol to visit NATO sailors," the Russian president said in March 2014, referring to the port city on the Crimean Peninsula.

NATO Secretary General Jens Stoltenberg spoke about the "troubling escalation of Russian military activities" before a meeting of NATO defense ministers on Oct. 8. (YouTube/NATO)

Even if Montenegrin membership of NATO would essentially be symbolic, that symbolism could prove potent for Russia. Montenegro would be the first new member of NATO since 2009, when two other former Balkan states – Albania and Croatia – were granted membership. Crucially, it would be the first new NATO member since relations between the West and Russia plummeted after the conflict in Ukraine last year.

In an op-ed for The Washington Post published last year, Michael Haltzel, a senior fellow at the Center for Transatlantic Relations at Johns Hopkins University, argued that by granting Montenegro membership, NATO could show that Article 10 of the North Atlantic Treaty – the article that allows the alliance to invite European states to join – is  "alive and well." Haltzel added that it would also "demonstrate that Moscow does not exercise a hidden veto over NATO membership and encourage other potential aspirants such as Finland and Sweden by showing that the door to membership remains open."

Fredrik Wesslau, director of the Wider Europe Program at the European Council of Foreign Relations, says that while there is no major strategic significance to Montenegro, granting it membership would strengthen "NATO's credibility as an alliance designed to underpin European security."

If the decision goes in Montenegro's favor, it would mean that almost the entire coastline of the Adriatic Sea, except for a small sliver of Bosnia, would be NATO territory. And while Montenegro might be a small state, it is a small state to which many Russians are attached. Perhaps because of a shared Slavic history (not to mention that Adriatic coastline), Russian tourists have flocked to Montenegro since it gained independence: In 2013, 300,000 were said to have visited the country, while local media have reported that Russian citizens may own up to 40 percent of the real estate in the country.

The Montenegrin government's desire for closer ties to the West has already put a strain on its relationship with Moscow: Last year, the country lent its support to European sanctions on Russia, a move that resulted in countersanctions on Montenegro from Moscow. Montenegrin President Filip Vujanovic has said that Russia "will understand" if the country does join NATO. At best, that comment seems hopeful.

While the events of 1999 may be past, they are not necessarily forgotten. According to Human Rights Watch, at least eight people in Montenegro were killed by NATO strikes that year. Over 28 percent of the country's population is ethnically Serbian and may be distrustful of NATO because of the conflicts over Kosovo and Bosnia and historical links to Russia. Opinion polls have shown large divisions over whether Montenegro should join the alliance, with those in favor appearing to have a slim but not altogether convincing majority.

For now, the decision seems to rest with NATO member states, and they appear to be split. The United States has offered some conditional support: The country's NATO envoy, Douglas Lute, told Reuters that if Montenegro can show an improvement in its corruption problems and prove NATO membership enjoys popular support in the country, Washington will back its bid.

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