 Russia's already-weak economy left it less able to withstand the challenges imposed by low oil prices and international sanctions.The Russian Central Bank's "erratic response" to the falling ruble has also been blamed for deepening the crisis.Since the Great Recession, yields on U.S. treasuries and other low-risk assets have decreased due primarily to the liquidity-trap and also unconventional stimulative measures by central banks, such as ZIRP and quantitative easing.