At the end of World War I in 1918, the Weimar Republic was proclaimed in Berlin. In 1920, the Greater Berlin Act incorporated dozens of suburban cities, villages, and estates around Berlin into an expanded city. This new area encompassed Spandau and Charlottenberg in the west, as well as several other areas that are now major municipalities. After this expansion, Berlin had a population of around four million. During the Weimar era, Berlin became internationally renowned as a centre of cultural transformation, at the heart of the Roaring Twenties.