Mr. Putin miscalculated in two ways. First, he was hoping that, as had been the case with his war against Georgia, the West would tacitly swallow his aggression against Ukraine. A unified response from the West was not something he expected. Second, since in his mind Russians and Ukrainians were one nation, Mr. Putin believed Russian troops needed barely to enter Ukraine to be welcomed with flowers. This never materialized.

What happened in Ukraine in 2014 confirmed what liberal Ukrainian historians have been saying for a long time: The chief distinction between Ukrainians and Russians lies not in language, religion or culture — here they are relatively close — but in political traditions. Simply put, a victorious democratic revolution is almost impossible in Russia, whereas a viable authoritarian government is almost impossible in Ukraine.

The reason for this divergence is historical. Up until the end of World War I (and in the case of western Ukraine, the end of World War II), Ukrainian lands were under the strong political and cultural influence of Poland. This influence was not Polish per se; it was, rather, a Western influence. As the Harvard Byzantinist Ihor Sevcenko put it, in Ukraine the West was clad in Polish dress. Central to this influence were the ideas of constraining centralized power, an organized civil society and some freedom of assembly.