Just as we wore down the old Soviet - causing it to spend itself out of existence, are the folks from China & Russia doing the same to us, via surrogates in the ME.
And 'Empire', as used contextually, is probably accurate.
Pax Britannia came and left. Now, Pax Americana may be on its way out.
Pax Americana will be around for a long time. No other power even comes close to matching our military and we are pulling away from most of the contenders at a rapid pace.