Opinion Ukrainian President Volodymyr Zelenskiy makes a statement in Kyiv, Ukraine, February 25, 2022. Ukrainian Presidential Press Service/Handout via REUTERS Russian President Vladimir Putin’s invasion of Ukraine — and the international condemnation it generated– contains key lessons for policymakers. They are lessons that should have been learned in past global crises but weren’t. However, the Ukraine crisis offers an opportunity to correct that mistake. A first lesson is that failure to firmly stand up to violations of international law as they occur convinces trespassers that they can get away with them. It emboldens violators to commit even more flagrant infringements....