Not necessarily. To go back to my example with China: they were unable to compete with the US in the military sense. They probably can now, but we don't know that for sure.
So China began to compete in the economic and political sense. Manufacturing development, BRI, etc. there didn't need to be conflict to collapse the hegemony.
In a multipolar world, we have the NK situation but on a global scale. With no undisputed champion, lots of people begin disputes. Which means wars. More military spending as a fraction of the global economy, as countries fight for dominance, instead of figuring out ways to economically outcompete each other.