For the second time in six years, Russian President Vladimir Putin has ordered Russian troops across an internationally recognized border to occupy territory. This fact must be stated plainly before any discussion of motives or consequences. Russian troops have taken Crimea and they are not leaving, despite the Ukrainian government's protests. Five hundred kilometers southeast across the Black Sea, Russian soldiers still occupy parts of Georgia—South Ossetia and Abkhazia—where they have been since Mr. Putin's 2008 invasion and de facto annexation.

Mr....