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| YEAR | DATE | EVENT | HEAD OF STATE |
| 1180 | Ecclesiastic Duchy of arcibishop of Koln | ||
| 1803 | Union to Markgraft of Brandenburg | ||
| 1807 | Kingdom | king Girolamo Bonaparte | |
| 1813 | Union to Markgraft of Brandenburg | ||
| 1918 | 9 november | German State | |
| 1945 | 23 may | Part of UK Occupation territory | |
| 1949 | 7 september | German State |