Washington (CNN) The country of Montenegro was thrust into the limelight after President Donald Trump was asked whether the US would come to the military aid of the most recent member of NATO.

Trump, in an interview on Fox News, appeared to cast doubt on his willingness to defend the country, calling the people of Montenegro "strong" and "aggressive," suggesting that its aggressiveness could draw the US into World War III due to the NATO's mutual security clause enshrined in Article 5 of the NATO treaty. It deems an attack on one member of NATO an attack on all countries in the alliance.

Article 5 -- which is defensive -- aims to deter potential adversaries from attacking NATO members. During the Cold War, the main concern was the Soviet Union, but in recent years, Russia's aggressive actions in Eastern Europe have been the focus of attention. Ukraine and Georgia, the two countries Russia has invaded in the past decade, are not NATO members.

"Our collective defense clause, Article 5, is unconditional and iron-clad. It means that an attack on one is an attack on all. President Trump has made clear that the US is fully committed to NATO and our Alliance is stronger than ever," a NATO official told CNN.

The southeastern European country is the newest member of NATO, having joined the alliance in 2017, the Alliance's first expansion since 2009 when Albania and Croatia joined.

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