Please see the following comments from Notre Dame's Michael Desch, director of the Notre Dame International Security Center.

"The current Ukraine crisis is, in part, the result of two bad decisions the U.S. took in the 1990s:  

The first was to expand NATO into the former Soviet space, in contradiction to assurances we gave the Soviets at the end of the Cold War. High-level officials in the Yeltsin government repeatedly told us (I was at one such meeting with his Foreign Minister) that doing so would undermine Russian democracy, which it certainly did. NATO welcomed its first new members in 1997 and Putin first came to power in 1999.

Second, the U.S.'s well-intentioned, but ultimately counterproductive, efforts in the mid-1990s under the Nunn-Lugar Act to denuclearize the the Ukraine, Belarus, and Kazakhstan left those states in a weak position vis-a-vis a much larger and more powerful Russia.

The way out of this crisis is the neutralization of Ukraine (and Georgia). If the former had a nuclear deterrent, that would be a much easier sell. Still, neutrality will not only defuse a potential great power crisis but it is not a bad strategy for weaker states stuck close to big powers. Just ask Finland, Austria, and the former Yugoslavia."