If Ukraine wins this war, some of its supporters abroad will no doubt be disillusioned to discover the nation’s darker side. Before the war, Ukraine ranked high on measures of perceived corruption — better than Russia, but that’s not saying much. Victory won’t make the corruption go away. And Ukraine does have a far-right movement, including paramilitary groups that have played a part in its war. The country suffered terribly under Stalin, with millions dying in a deliberately engineered famine; as a result, some Ukrainians initially welcomed the Germans during World War II (until they realized that they, too, were...