Why one nation cannot fight the whole world

What is the least convincing kind of what-if scenario discussed here?

Scenarios in which one state fights the entire world fail because even a great power cannot cover every front or sustain the required manpower and logistics.

Sincere student questions are distinguished from counterfactuals advanced by people who should recognize their logistical limits. The recurring example is a single nation taking on the entire world. Whether the country is imagined as China or the United States, it cannot place forces everywhere at once or sustain simultaneous fronts indefinitely. China attacking every neighboring state illustrates how even a very large population runs into finite troop numbers. Alternate history still has to account for transport, geography, manpower, and simultaneous commitments.