The move has made Russia furious, threatening the small country with economic and political retaliation.
The tiny Balkan state of Montenegro is joining the Western military alliance NATO on Monday in a historic turn that has made the Kremlin furious.
Despite the Russian anger and a deep split within the nation of some 620,000 people over the issue, Montenegro is formally becoming the 29th member of the Western military alliance at a ceremony in Washington on Monday.
To get there, Montenegro has stood up against its former ally Russia, which has sought to maintain strong historic, political and cultural influence in the Slavic country it considers a special zone of interest.
Bringing Montenegro into NATO further diminishes Russia's influence in southeast Europe, and blocks it from the so-called "warm seas" in Europe that could be used as staging grounds for military interventions in the Middle East.
Economic, political retaliation
Russia has threatened economic and political retaliation, including a campaign to undermine the Montenegrin tourism industry, which relies heavily on Russian visitors.
It has also banned imports of Montenegrin wine and recently deported a ranking official from a Moscow airport.
Russian foreign ministry spokeswoman Maria Zakharova recently warned potential Russian tourists that "there is an anti-Russian hysteria in Montenegro."
"We do not rule out the possibility of provocations, arrests for suspicious reasons or extradition to third countries" of Russians, Zakharova said.
Her claim was dismissed by the president of the Russian-speaking diaspora in Montenegro, Alexander Khrgian, who runs his law office in the coastal resort of Budva.
He said that about 15,000 Russian-speaking people who permanently live in Montenegro feel safe.
"I have been living in Russia for 25 years and now I am here for more than 10 years, and we love Montenegro. It is a wonderful country with wonderful climate," he said.
"People know that Russia and Montenegro have very close cultural links. That is why we are here like at home."
Russia allegedly behind failed coup
Montenegro says Moscow was behind a foiled coup attempt in October that allegedly targeted former Prime Minister Milo Djukanovic, who was the driving force behind the country's NATO bid. Russia denies involvement.
"Therefore, our goal is to bring even more Russian tourists."
On the eve of the NATO accession, Montenegrins don't seem interested in their country's historic move and many of them want good relations with both Russia and the West.
"If we were neutral all the time, why shouldn't we continue with it so that we keep good relations with America, Russia and all the other countries?" said Mirko Bozovic from Podgorica.
The pro-Russian opposition Democratic Front, whose top two leaders were indicted over allegedly planning the Russia-orchestrated coup, said the day when Montenegro joins NATO is one of the saddest days in its history.
"Today, Montenegro is being annexed like never before in its history," official Strahinja Bulajic said.