The most populous (with 18 million people) and westernmost (bordering Belgium and the Netherlands) of Germany's federal states, North Rhine-Westphalia is one of Europe's most highly industrialized areas, with an impressive 30 cities of more than 100,000. Cologne is the district's biggest city, and the capital is Dusseldorf. Bonn, the former capital of West Germany, is also here. All three are part of the Rhine-Ruhr region of nearly 12 million people, one of Europe's biggest metropolitan areas.