"While he laughed at the idea of Russia presenting a national security threat, Gates said he was concerned about the global impression – identified by Hagel – that the U.S. may not be as much of a global power as it once was.
“Our allies are watching to see whether we will be there for them they are challenged, internally or externally. Other countries, whether it’s Russia, china, Iran or North Korea are looking to see if what they perceive as withdrawal from international leadership presents them with some opportunities down the road.”
He added, “If there is a perception that the U.S. is withdrawing back home, then other countries are going to look for opportunities to advance old nationalist ambitions or satisfy revanchist claims. In the end, he predicted, the world faces increasingly frequent conflict if the U.S. does not assert its role as “guardian of the international order.” "
http://finance.yahoo.com/news/putin-rise-highlights-u-descent-202000820.html
But it is a fair point that reduced US power may result in instability.