Soviet expeditions were sent almost yearly from 1923. Franz Josef Land had been considered "terra nullius" – land belonging to no one – but on 15 April 1926 the Soviet Union declared its annexation of the archipelago. Emulating Canada's declaration of the sector principle, they pronounced all land between the Soviet mainland and the North Pole to be Soviet territory. This principle has never been internationally recognized. Both Italy and Norway protested. Norway was first and foremost concerned about its economic interests in the area, in a period when Norwegian hunters and whalers were also being barred from the White Sea, Novaya Zemlya and Greenland; the Soviet government, however, largely remained passive, and did not evict Norwegian hunting ships during the following years. Nor did the Soviets interfere when, in 1926, several foreign ships entered the waters in search of the vanished airship "Italia".