2008 NATO summit in Bucharest.
“This is where [Putin] gave his extraordinary speech saying Ukraine was an artificial country and the greater part of these lands historically belonged to Russia.”
At the summit the Kremlin warned it would respond militarily to moves by Ukraine or Georgia to join the NATO alliance: months later Russian forces seized on a provocation from Tbilisi and invaded Georgia.
http://www.politico.com/magazine/story/2014/10/vladimir-putins-coup-112025_Page3.html#.VEk7DfmsUfw