Complex sentence: They had moved from being a collection of independent tribes to an effective confederation known as the Māori King Movement, which was centred on the Waikato region, but which had influence over large areas of the North Island.
Split into simpler sentences: They had moved from being a collection of independent tribes to an effective confederation. This was called the Māori King Movement and was largely centred on the Waikato region, but had influence over large areas of the North Island.