Politicized revisions of the past help antidemocratic leaders justify their actions while sowing divisions at home and abroad.

Fifty years ago today, a military force led by the Soviet Union burst across the border into Czechoslovakia to crush the Prague Spring—a nonviolent reform movement aimed at forging a democratic alternative to communist totalitarianism. The soldiers who participated in Operation Danube had been told that a CIA-inspired coup was under way, that elements within the Czechoslovak leadership had “requested fraternal aid” to restore order, and that the Czechs and Slovaks would treat them as liberators.

The Soviets later maintained the essence of these lies as official history, which their political heirs continue to promote to this day. A documentary aired on Russian television in recent years justified the invasion of Czechoslovakia in part by falsely claiming that it preempted a NATO attack.

In Prague itself, the 50th anniversary of the Soviet invasion will be marked by open discussions about the reform movement’s leading figures, its contribution to freedom, and the reasons for its failure. But the governments in some countries that suffered under Soviet occupation have ironically embarked on their own ambitious campaigns to rewrite history—especially surrounding the fight against communist rule—as a means of justifying modern-day power grabs.

In Hungary, where the right-wing government led by Viktor Orbán has crushed judicial independence, transformed once-lively media into propaganda instruments, and manipulated the electoral system to minimize the chance of defeat…