Complex sentence: Founded in the 16th C. Developed due to its fishing and fish processing industry and also from the growth of tourism and Keflavik International Airport which was built by the US during the 1940s.
Split into simpler sentences: Founded in the 16th century, Keflavík developed due to its fishing and fish processing industry. Later its growth continued from tourism and Keflavík International Airport which was built by the US during the 1940s.