As Russian President Vladimir Putin's forces took over Ukraine's Crimean peninsula in early 2014, the interim Ukrainian government was debating whether or not to fight back against the "little green men" Russia had deployed. But the message from the Barack Obama administration was clear: avoid military confrontation with Moscow.
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Looking back today, many experts and officials point to the decision not to stand and fight in Crimea as the beginning of a Ukraine policy based on the assumption that avoiding conflict with Moscow would temper Putin's aggression. But that was a miscalculation. Almost two years later, Crimea is all but forgotten, Russian-backed separatist forces are in control of two large Ukrainian provinces, and the shaky cease-fire between the two sides is in danger of collapsing.

http://www.bloombergview.com/articles/2015-08-21/u-s-told-ukraine-to-stand-down-as-putin-invaded