North Rhine-Westphalia (German: Nordrhein-Westfalen) is the most populous state of Germany, as well as the fourth largest by area. North Rhine-Westphalia was formed in 1946 as a merger of the northern Rhineland and Westphalia, both formerly parts of Prussia. Its capital is Düsseldorf; the biggest city is Cologne. Four of Germany's ten biggest cities--Cologne, Düsseldorf, Dortmund, and Essen--are located in North Rhine-Westphalia. The state is currently run by a coalition of the Social Democrats (SPD) and Greens.
The state of North Rhine-Westphalia was established by the British military administration's "Operation Marriage" on 23 August 1946, by merging the province of Westphalia and the northern parts of the Rhine Province, both being political divisions of the former state of Prussia within the German Reich. On 21 January 1947, the former state of Lippe was merged with North Rhine-Westphalia. The constitution of North Rhine-Westphalia was then ratified through a referendum.