The "Union with Denmark" refers to the historical political union between the Kingdom of Denmark and the Kingdom of Norway, which lasted from 1380 to 1814. This union began when King Haakon VI of Norway married Margaret I of Denmark, leading to a shared monarchy. Although Norway maintained some degree of autonomy, Denmark held significant power over the union. In 1814, the union ended when Norway entered a brief union with Sweden after the Napoleonic Wars. The Treaty of Kiel marked this transition, and Norway adopted a new constitution, asserting its independence while still maintaining a connection with Denmark through cultural and historical ties.