Byzantium was in decline for seven centuries until the Ottomans pulled the plug. Rome was in decline for several centuries prior to its sacking.
Climate change and the accompanying plagues, droughts, famines, and calamities that accompany it might accelerate and exacerbate the state's capacity and willingness to respond to these crises, but all it might mean is that this is a new normal added to the reproleterization of American life.
I don't really have a point but it is just a thought that I (perhaps others) are going to have to accept that future, and that is a kind of new world I am unsure as to how to adapt to.
But how much of that is because of their relationship with the US? They wouldn't have remained that powerful if they weren't a part of this American-centered nexus.
Both France and the UK has its own fairly powerful military. France maintains a relationship with African nation's only comparable to how the US treats latin america.