When I became president of Ukraine a year ago this month, Crimea had been annexed, the country was standing on the brink of war and—after more than 20 years of Soviet-style governance, endemic corruption, cronyism and inefficient policy—our economy was sliding into decay.

Now, another revolution is under way. The struggle this time is just as vital as during the 2013-14 pro-democracy Revolution of Dignity on the Maidan in our capital city of Kiev. It has the potential to move Ukraine closer to the European future that the...