For those trying to keep up with fast-moving events in Ukraine, it may be helpful to consider some lessons of history. Mistakes made in the past week, added onto developments covering the last two or three centuries, have left the United States and its European allies (in particular the largest of them, Germany) unable to prevent Vladimir Putin’s Russia from absorbing an as-yet-undetermined part of a theoretically independent Ukraine.

One lesson of history is contained in the aphorism, “If you set out to take Vienna, take Vienna.” It’s attributed to Napoleon, who in fact took Vienna twice, and whose capacity to “surprise and outmaneuver his opponents,” as the Wall Street Journal’s Walter Russell Mead writes, came from a willingness “to assume risks they would never consider, and so to attack in times and ways they can neither imagine nor plan for.” Putin, another upstart from an obscure backwater, seems to share the same trait.