Before the war, Greenland was a tightly controlled colony of Denmark, otherwise closed off to the world. After the invasion of Denmark on 9 April 1940, Greenland was left on its own, because the Royal Navy seized any ships arriving from Axis-controlled Europe. The United Kingdom and Canada initially laid plans to occupy points of interest on the island, but the United States, still neutral, firmly rejected "third party" intervention there. The sheriffs ("landsfogeder") of South and North Greenland, Eske Brun and Aksel Svane, invoking the emergency clause of a 1925 law specifying how Greenland was ruled, declared Greenland a self-ruling territory, believing this to be in the best interests of the colony as Denmark was occupied by Nazi Germany. This step was taken in coordination with the Danish ambassador to the United States, Henrik Kauffmann, and the US State Department, and comported with the American declaration of 1920 that no third nation would necessarily be accepted as a sovereign in Greenland. This diplomatic stance was seen as an extension of the Monroe Doctrine.