There are six reasons Americans should feel good that Montenegro — a tiny state of little over 600,000 inhabitants with a military of about 2,000 — will become the 29th NATO ally, as ratified by alliance foreign ministers earlier this month.

First, and most obvious: with tension between Russia and the West at center stage, NATO and Montenegro are denying Russia a veto over their policy. We are standing strong in the face of Russian intimidation. Last fall, Russian Foreign Minister Lavrov declared NATO’s expansion to include Montenegro “a mistake, even a provocation” and an “irresponsible policy.” And after Russia invaded Ukraine, when Montenegrin Prime Minister Djukanovic visited Washington and took a public stand with the United States and European Union, Russian officials poured vitriol on him personally, while offering bribes for military access to Montenegro’s ports, providing financial and other support to opposition groups against NATO membership, and imposing counter-sanctions on Montenegrin agricultural products. Last week, Russia declared that they would cancel cooperative “projects” with Montenegro; it is unclear what Moscow meant since the two governments have no current notable joint projects.

But Montenegro is standing firm. Some major Russian private investors, such as oligarch Oleg Deripaska, who invested in Montenegro’s aluminum industry, have been forced out of Montenegro. Its Ministry of Defense is moving to modernize its military with U.S. or European equipment — for example, gradually ditching aircraft that require Russian spare parts and maintenance. Montenegro’s determination and NATO’s decision stand in defense of the sovereign right of states to determine their political, military and economic associations and as a counter to Russian bullying.

Second, this is another step in the U.S.-launched effort to bring stability to the Balkans, going back 20 years to the signing of the Dayton agreement, which brought peace to Bosnia. This work is far from complete. Bosnia remains a weak state, wrought with ethnic political tension. Serbia has yet to recognize Kosovo as a sovereign state. Macedonia is politically and ethnically polarized. But there has been no war in the Balkans since the Kosovo war, which NATO brought to a finish after about three and a half months in 1999. Montenegro becomes the third former Yugoslav state to join after Slovenia (2002) and Croatia (2009 with Albania). As the Balkan state that prides itself on positive relations with its neighbors, NATO membership acknowledges the significance of that achievement for the youngest Balkan state, founded only in 2006 in a peaceful split with Serbia. And this will only serve to encourage Serbia in its EU-led normalization with Kosovo, since Belgrade’s motivation is also obtaining membership, albeit in the EU, not NATO (for the moment; this will likely change).

Third, this NATO expansion, the first since 2009 (and the first for the Obama administration) will provide much-needed encouragement and pressure on the remaining three formally acknowledged NATO aspirants Bosnia and Herzegovina, Georgia, and Macedonia (with Ukraine as a longer-shot aspirant). The seven-year lapse after the expansionary burst of the 2000s left many in the Balkans and Georgia wondering whether NATO’s so-called “Open Door” had not quietly been closed. Last week’s decision proves this is not the case. Bosnia and Macedonia still have much work to do in order to be ready for NATO membership and the latter has the formal requirement to come to an agreement with Greece over the name of the country (this is the sole stated requirement, but given political dynamics in Macedonia, NATO may also demand more reform). Georgia is ready in many ways for membership; the chief obstacle is Russia’s military occupation of 20 percent of its territory.

Fourth, including Montenegro seals off the entire Adriatic coast for NATO and prevents — in the words of one senior NATO military official — “Kaliningrad on the Mediterranean.” While NATO faces Russian air defenses and missiles in its Baltic Sea enclave, we can now avoid this in the Adriatic; Montenegro will no longer be vulnerable to subtle Russian military occupation, exercised through access to bases and stationing of Russian personnel and equipment.

Fifth, this is good news for Montenegro. As result of NATO requirements, and in support of their membership bid, they professionalized their military. Among other things, the government revamped military education and training and established a military intelligence agency separate from domestic intelligence services. Since 2010, their forces have deployed with U.S. troops to Afghanistan, where they gained valuable military interoperability with NATO. And they were forced to take some action against corruption and to strengthen rule of law. Here, this is only a start; much more will need to be done, perhaps in a more secure post-accession political environment.

Sixth, and finally, as Damon Wilson, Executive Director of the Atlantic Council has pointed out elsewhere, NATO has demonstrated and boosted its own confidence through its invitation to Montenegro: “You don’t enlarge if you don’t have a sense of confidence in your institution.”

This December 2 brought — along with the horrific San Bernardino attacks — some good news for Americans: we have another formal ally in our war against radical Islamic terrorism and another demonstration of the appeal of free-market capitalism, democracy and collective security built on sovereignty and consensus.