On Wednesday, foreign ministers extended an invitation of NATO membership to Montenegro, a small nation in the Balkans. The decision to offer Montenegro membership will strengthen the NATO alliance, improve regional security in the Balkans, and most importantly send a clear signal that NATO remains committed to its open door policy. It also shows other countries in the region that if they reform their systems of governance, economies, and militaries, NATO membership is possible.

Montenegro, a small country located in the Balkan Peninsula, formally began a Membership Action Plan (MAP) in 2009 and made good progress. The Wales Summit Declaration issued in Sept. 2014 lauded Montenegro’s progress in implementing reforms and agreed to “open intensified and focused talks with Montenegro” on membership. Montenegro has been a steadfast ally, participating in the NATO International Security Assistance Force (ISAF) mission in Afghanistan from 2010-2014, and currently contributes to NATO’s Resolute Support Mission in Afghanistan helping train, advise, and support Afghan security forces.

NATO’s open door policy for qualified countries has contributed greatly to trans-Atlantic security since the first round of NATO enlargement in 1952. While small in absolute terms, Montenegro has proven its commitment to the alliance, at one time spending more than 10 percent of its defense budget to support its contribution to ISAF. The offer of NATO membership rewards Montenegro for its steadfastness and will ultimately help further solidify trans-Atlantic security by providing an anchor of stability in a historically volatile region of Europe.

As Heritage’s Luke Coffey has noted, “Montenegro would be a welcome addition to the NATO alliance, and its accession to full membership would contribute to continued regional stability.” Montenegro’s invitation also shows that Russia does not have a veto over NATO enlargement and is a blow to Russia. Last year Montenegro turned down a Russian request to host a Russian naval base.

While Russia has described any further NATO enlargement as a “provocation,” no third party should have a veto over the decision of the NATO member-states. Currently, three other nations—Bosnia and Herzegovina, Georgia, and Macedonia—are candidate countries for NATO membership. The U.S. should support these nations in their path to NATO membership and should in particular champion Macedonia joining; Macedonia met all the criteria for membership in 2008 but has been stymied from joining due to a name dispute with Greece.

The announcement that Montenegro will be offered much deserved membership in NATO is a welcome one. NATO’s open door policy is an integral component of the alliance’s strength. Montenegro’s inclusion in the alliance bolsters regional and trans-Atlantic security and sends a strong message of strength to friend and foe alike.