In 2020, just 246 people tried to sneak into Poland from Belarus through the marshy wetlands on the border, according to the Polish government’s records. There was a pandemic on, after all. But over the following year, almost 40,000 migrants from Syria, Somalia, Iran, Afghanistan, India and other countries crossed or attempted to cross this frontier. Those migrants didn’t end up in Belarus by accident. Some were carrying Russian visas or entry stamps. Russia and its ally — some would say lackey — Belarus were, in effect, importing migrants, delivering them to the Polish-Belarusian border and telling them to head...