Before the end of the 1930s, the Arctic had not been considered a zone of particular strategic interest due to its climate and difficulty of access. However, as developments of sea and air technology facilitated access, the Arctic North would open up to become another front in the Second World War. The Soviet invasion of Finland and German invasion of Norway and Denmark marked an unprecedented militarization of the zone, and following the German invasion of the Soviet Union, Murmansk provided Allied supply ships from the United Kingdom, an important avenue through which the Allies supplied the Soviets.