Which country was the last to join NATO before 2020?

Montenegro was the last country to join NATO before 2020, officially becoming a member on June 5, 2017. This marked an important step in the alliance's expansion into the Balkans, reflecting NATO's ongoing commitment to collective defense and regional stability. Montenegro's membership added to the number of countries within the alliance, further enhancing its strategic capabilities.

Looking at the other countries listed, North Macedonia joined NATO more recently, on March 27, 2020. Sweden and Finland, while currently not NATO members, have maintained partnerships with the alliance and have considered membership, particularly in light of rising security concerns in Europe. Thus, Montenegro's entry into NATO stands as the most recent before 2020, solidifying its role in the coalition at that time.