The islands were first used as a whaling base in the 17th and 18th centuries. After this, they were abandoned. Coal mining started at the beginning of the 20th century, and several permanent villages were built. The Spitsbergen Treaty of 1920 states that Norway is in control of Svalbard. The 1925 Svalbard Act made Svalbard part of Norway. These treaties also set out rules that economic activities could be done freely and that no military activities can take place. There are only two mining companies, one Norwegian and one Russian. Research and tourism are important industries. There are no roads to connect the settlements. Instead, snowmobiles, aircraft and boats serve as transport. Svalbard Airport in Longyearbyen is the main airport.