After periodic political unrest, particularly in 1848, Hamburg adopted in 1860 a semidemocratic constitution that provided for the election of the Senate, the governing body of the city-state, by adult taxpaying males. Other innovations included the separation of powers, the separation of Church and State, freedom of the press, of assembly and association. Hamburg became a member of the North German Confederation (1866–1871) and of the German Empire (1871–1918), and maintained its self-ruling status during the Weimar Republic (1919–1933). Hamburg acceded to the German Customs Union or Zollverein in 1888, the last (along with Bremen) of the German states to join. The city experienced its fastest growth during the second half of the 19th century when its population more than quadrupled to 800,000 as the growth of the city’s Atlantic trade helped make it Europe’s second-largest port. The Hamburg-America Line, with Albert Ballin as its director, became the world’s largest transatlantic shipping company around the start of the 20th century. Shipping companies sailing to South America, Africa, India and East Asia were based in the city. Hamburg was the departure port for many Germans and Eastern Europeans to emigrate to the United States in the late 19th and early 20th centuries. Trading communities from all over the world established themselves there.