NATO and the rest of the member nations will still have to give sign off for Montenegro to formally join.
Previously, Senator John McCain stirred drama on the floor of the Senate over Montenegro's bid to enter NATO. When Rand Paul, a Republican senator from Kentucky, said he would object to Montenegro joining NATO, McCain lashed out, "The senator from Kentucky is now working for Vladimir Putin."
In response to the treasonous allegation, Paul responded in a statement later that day that Washington has already sent troops to be stationed in "dozens of countries," and "is actively fighting in Iraq, Syria, Libya and Yemen (with the occasional drone strike in Pakistan)."
"The United States is pledged to defend 28 countries in NATO. It is unwise to expand the monetary and military obligations of the United States give the burden of our $20 trillion debt," Paul said.
Montenegro's place in NATO would mark the alliance's first expansion into Southeast Europe in six years.
Annexing the Balkan nation into NATO threatens to destabilize the region, Russian ambassador to Serbia Alexander Chepurin told Sputnik.
"Attempts to push several Balkan nations to NATO, to change their genetic code, without asking the people's opinion — are the issue that destabilize the situation in the Balkans," Chepurin said.
The final vote count in the Senate was 97 in favor and two in opposition.