Complex sentence: The company established settlements at Wellington, New Plymouth, Wanganui and Nelson and also planned settlements at Christchurch and Dunedin, reaching the peak of efficiency about 1841 before ceasing activity in 1858.
Split into simpler sentences: The company established settlements at Wellington, Nelson and Wanganui and was also involved in the settling of New Plymouth. It also planned settlements at Christchurch and Dunedin, reaching the peak of efficiency about 1841 before ceasing activity in 1858.