Key Points

>Turkey's Erdogan has doubled down on his opposition to Sweden and Finland joining the NATO alliance, in a move some analysts say is aimed at gaining concessions.

>NATO ascension for a new member state requires consensus approval from all existing members.

>Turkey, which joined the alliance in 1952, is a crucial player in NATO, boasting the second-largest military in the 30-member group after the United States.

Turkish President Recep Tayyip Erdogan has doubled down on his opposition to Sweden and Finland joining the NATO alliance, a move that would be historic for the two Nordic countries in the wake of Russia's invasion of Ukraine.