A Singleton is a world order in which there is a single decision-making agency at the highest level. See https://nickbostrom.com/fut/singleton.html for a succinct summary, and some analysis of possible pros and cons.
Let's assume extraordinary technological breakthroughs that may cause one entity (a state or a financial company) to have massive economic dominance (say: slow AI takeoff, free energy from fusion reactors, advanced nanotech) or massive offensive dominance (cyber-warfare capabilities, undetectable nuclear weapons, DNA-targeted bioweapons). In this case, that entity may decide to claim power over civilization.
Considering that it is possible that a singleton is unavoidable, and that it may be easy to remain locked in to such a governance, it is of obvious importance to the future of humanity.
The main idea I want to bring out in this post is that the formation of a singleton in the near future is perhaps likely (even without strong AI or a great power war), and I'd like to see further discussion on this topic.