Below is the evolution of NATO members up to 2004:
In light of the Kremlin's orchestrated aggression in the northern Baltic's, a uniformed, NATO, nuclear protective missile shield is more then required from Estonia to Bulgaria, in order to hopefully prevent, plus guarantee a swift NATO response to any future full scale Russian land invasions or nuclear attacks directed at 'former' Moscow controlled, now free, Eastern European nations.
Thanks for the NATO progression map.
Putin is testing NATO and trying to reduce tensions at home by these adventures.