Various groups of Pākehā arrived in this country between 1800 and 1840, and for different reasons. These groups included explorers (although they pre-dated the 19th century), sealers, whalers, traders, and missionaries. All these groups had different purposes and therefore different effects on the local Maori population. The explorers mapped the country and announced its existence; sealers harvested seals without much effect on local Maori; whalers hunted whales creating "Pacific hell"; and the missionaries, who came with the intention of changing the Maori, had the greatest impact of all. The first Europeans to visit New Zealand were explorers. Abel Tasman, who arrived in 1642, was first, followed by James Cook in 1769. Although none of these voyages occurred in the period 1800-1840, Cook's informative journals were the catalyst for future voyages to New Zealand, as detailed the abundance of plant and animal life found here. Because the explorers simply arrived, mapped and left, their main impact on Māori was secondary, as many other Pākehā arrived in New Zealand thanks to information contained in Cook's journals. The first group of Europeans to be "summoned" by Cook's journal were the sealers. . Sealers came from America, Australia and Britain to obtain sealskins to exchange for Chinese tea. This was the first step that connected New Zealand to the world economy. Sealers had minimal impact on Maori due to their location: seals congregated near the bottom of the South Island, where very few Maori lived. The sealers lived a very hard life because they were abandoned and then left to fend for themselves for several years. The seal trade reached its peak between 1803 and 1810, when major groups of Pākehā arrived in New Zealand. Explorers, even though they came before this period, discovered this country and revealed its existence to others. Sealers arrived to make fur hats. The whalers formed the town of Kororareka and the missionaries began the conversion of the Maori to Christianity. All these Pākehā groups influenced the local Māori population; however, explorers and sealers had a very small impact, while whalers and missionaries had a larger one. The intent for change and interaction with large numbers of Maori were the reasons for this: explorers and sealers were on the fringes and had little or no contact with the Maori. The whalers, on the other hand, had a lot of contact with the Maori, as they used them to help in the processing of the whales, and the missionaries, whose intent was to convert the "savages" to Christianity, had a great effect because of their purpose..