Complex sentence: After all, the King was a king by virtue of the approval of the Chiefs and not in spite of them and while in Maniapoto the King was in essence in their kingdom where their mana reigned supreme.
Split into simpler sentences: After all, the King was a King by virtue of the approval of the Chiefs and not in spite of them. While in Maniapoto the King was in essence, in their kingdom where their mana reigned supreme.