The invasion of Ukraine by Russian forces over a month ago shouldn’t be a surprise. The two nations share a long and complicated history which has in the past 10 years included armed conflict over the annexation of Crimea by Russia in 2014 and with Russian backed separatists in Eastern Ukraine. There are other issues too–like the US-led expansion of NATO into former Warsaw Pact nations after the breakup of the USSR in 1991. Ukraine’s interest in joining NATO has only increased the tension. Here’s one attempt to explain the history to better understand the current crisis.