Across the Atlantic, the U.S. continued to be the big dog until certain cracks began to show. 9/11 undermined the U.S.' impenetrability, the 2008 recession put a mountain of doubt into the way the West was running things, wars like Iraq and Afghanistan sowed the seeds of doubt that the U.S. was just another invading colonialist jerk. Each of these events, and many more, undermined global confidence as well as Russian assurance in the global community system.
The E.U., not necessarily intentionally, was also seen as a very aggressive alliance against the former USSR, and in turn, Russia. The tide of a unified E.U. moving east towards their former lands made Russia very aware that the former glory they once held was being sacrificed and swallowed up by a system they saw as broken, foreign and dangerous.
Russia's economy was doing well and Putin is essentially president, or prime minister for life, so little pushes into its former colonies were met with a concerned tut tut from neighbors, but overall were ignored in favor of a cordial and unified G8. Putin figured he could use the West's reticence toward developed aggression by pushing the line ever further. He overestimated this line by gambling that his Sochi Olympics would balance out with his shadow invasion of Crimea. Needless to say, this didn't go well.