Which NATO member joined the alliance in March 2020?

North Macedonia is indeed the NATO member that joined the alliance in March 2020. This accession followed a prolonged process involving significant reforms in its defense and security structures. The country's path to NATO membership was significantly influenced by the Prespa Agreement in 2018, which resolved a long-standing naming dispute with Greece, thus paving the way for North Macedonia to join the alliance. This event marked a significant expansion of NATO's presence in the Balkans, enhancing regional security and cooperation among NATO allies.

The other options, while relevant in the context of NATO and its member states, do not fit the criteria of being the nation that joined in March 2020. Finland and Sweden have made strides towards NATO membership and have engaged in partnership programs, but they did not achieve membership by that date. Iceland, as a founding member of NATO, has been part of the alliance since its inception and is not a new addition.