military acknowledged New Zealand sovereignty during World War II operations. The Cook Islands became a self-governing island nation in free association with New Zealand in 1965, and the US relinquished any last claims to the islands when it signed the 1980 Cook Islands–United States Maritime Boundary Treaty. Economy In general terms, the northern group is the less well economically developed of the two chains, having far less connection with the rest of the world than the southern chain. A compounding factor is the limited economic resources of the islands; though fishing is important to the group, the coral soil is of poor fertility and fresh water is generally in poor supply. The population is in decline, having reduced from over 2000 in the early 1960s. The higher susceptibility of the chain to tropical cyclones (and the propensity for greater damage due to its low-lying nature) has also caused considerable hardship, with severe damage being recorded after Cyclone Percy in 2005. The vulnerability of the chain to global warming (for the same reason) has also not encouraged economic development of the islands. References Further reading Wheeler, T., and Keller, N. J., (1994) Rarotonga and the Cook Islands. Hawthorn, VIC, Australia: Lonely Planet. Landforms of the Cook Islands Archipelagoes of the Pacific Ocean Cook Islands Islands of the Cook Islands