As the Free Imperial City of Cologne it was one of the centers of the Hanseatic League in the early modern period.
Most of the city was destroyed in the bombing of Cologne in World War II, so it was of limited importance in post-war West Germany. It had returned to its pre-war population by 1959, by which time Düsseldorf was the political center of the state of North Rhine-Westphalia, and Bonn was the (provisional) capital of the Federal Republic.
In the late 20th century, Cologne grew into a center of the sprawling Rhine-Ruhr metropolitan area, with some 12 million inhabitants, just over one million of whom live in Cologne proper (as of 2012), making the city the fourth largest in Germany (after Berlin, Hamburg and Munich).
