The move uptown started in the 1920s when rents in Maiden Lane began increasing drastically as finance and insurance companies moved into the Financial District. The district grew in importance when Nazi Germany invaded the Netherlands and Belgium, forcing thousands of Orthodox Jews in the diamond business to flee Amsterdam and Antwerp and settle in New York City. Most of them remained after World War II, and remain a dominant influence in the Diamond District. By 1941, the Diamond Dealers Club—an exclusive club that acts as a de facto diamond exchange and has its own synagogue—officially made the move up to midtown as well.