Authorities in Hamburg, the second-largest city in Germany, have begun confiscating private dwellings to ease a housing shortage — one that has been acutely exacerbated by Chancellor Angela Merkel’s decision to allow more than two million migrants into the country in recent years. City officials have been seizing commercial properties and converting them into migrant shelters since late 2015, when Merkel opened German borders to hundreds of thousands of migrants from Africa, Asia and the Middle East. Now, however, the city is expropriating residential property units owned by private citizens. In an unprecedented move, Hamburg authorities recently confiscated six residential...