At the turn of the 20th century, Norway’s economy rested largely on the primary sector, whether fishing, agriculture or forestry. A small industrial base, located mostly in the south, and limitations imposed by nature on agricultural development limited job creation, thus leading to out-migration, in particular to North America. Prospects for the economy began to change at the end of the 19th century with the development of hydro-electric power, harnessed across the country by numerous waterfalls. Cheap electricity facilitated the expansion of metallurgical and chemical manufacturing, especially aluminium, iron alloys and fertilisers. Small cities by the fjords became central to Norwegian industry. At the same time big companies became crucial for employment and regional development in many parts of the country. In the depression after WW I, expansion in electricity production and metal industries slowed down, but became later more specialised. After WW II the state established a Norwegian Iron Works in Mo i Rana, based on regional electricity production and local iron ores. Iron from the Kiruna mines in Northern Sweden was exported from the ice free harbour of Narvik. The control of these strategic resources was a major challenge during World War II, as showed precisely by this famous battle. Their exploitation than sparked the growth of shipbuilding at the benefit of the southern part of the country.