NATO Accession
On March 29, 2004, Bulgaria, Estonia, Latvia, Lithuania, Romania, Slovakia and Slovenia joined NATO at the 2004 Istanbul summit. Albania and Croatia joined the alliance in 2009. Macedonia had been expected to join in 2009, but because of the Macedonia naming dispute, Greece vetoed Macedonia's invitation, leaving it as the only former member of the Vilnius group not to be a member of NATO by 2009.
Read more about this topic: Vilnius Group