I view the expansion & contraction of empire as natural & beneficial, although probably in the long run we'll have fragmentation, especially from present GAE model

Expansion occurs when military technology favors offense, allowing large territory to be quickly amassed & bound into empire. Usually the winning faction enjoys organizational & economic advantages, as in the Roman & British empires.

Fragmentation occurs when military technology favors defense, allowing smaller powers to defend themselves against aggressors and entropy to wear away at empires.

The American world empire is a special case. Since industrialization, the trend is towards attrition (defensive) warfare and away from maneuver. For example, the nations involved in WW1 expected to quickly amass vast territory via cavalry maneuver, but were instead cut down by machine guns, leading to the attrition war. In WW2, the Americans enjoyed a technological & economic lead provided by the previously-free (but rapidly socializing) economy, as well as a brief period in which mechanized warfare (tanks & air power) was unmatched. We now possess very cost-effective anti-tank and anti-air systems (a missile costing tens of thousands of dollars can be carried & fired by a single soldier to destroy vehicles costing tens of millions)

So America conquered the world (along with its ally & former puppet the Soviets). But they did it not on organizational brilliance, but on industrial, technological & economic might. The rest of the world has industrialized, largely caught up to modern technology, and US economic might is for the moment largely a paper tiger. US financial power relies on world acceptance of its currency and capacity to bully others into sanctions - not on industrial superabundance.

Fragmentation from the US empire seems likely.

Moreover, I see no reason for the general trend of attrition warfare to reverse, or for other loci of hard power to be spared.

Finally, trade is more efficient than war, creating another element of financial incentive that favors fragmentation - when it does occur, the cost of violent dispute is escalated. In an increasingly productive, specialized, and interdependent world, those costs are increasingly magnified.