National and international migration into the city has a long history. In 1685, after the revocation of the Edict of Nantes in France, the city responded with the Edict of Potsdam, which guaranteed religious freedom and tax-free status to French Huguenot refugees for ten years. The Greater Berlin Act in 1920 incorporated many suburbs and surrounding cities of Berlin. It formed most of the territory that comprises modern Berlin and increased the population from 1.9 million to 4 million.