Only three remaining super powers remain, each competing for the scant resources left on the planet after dozens of nuclear wars have rendered vast swaths of the world uninhabitable wastelands.
The polar ice caps have melted 20 times due to nuclear wars and all of the big cities have crumbled.
Roughly 90% of the worlds population (at its peak 2000 years ago) has died either from nuclear annihilation or famine caused by the global warming that has left absolutely zero arable land to farm
"I was forced to do away with democracy roughly a thousand years ago because it was endangering my empire. But of course the people hate me now and every few years since then, there are massive guerrilla uprisings in the heart of my empire that I have to deal with which saps resources from the war effort."
The military stalemate is so tight and balanced that no other action is possible except the construction of more tanks. This also means that cities are not only tiny towns full of starving people, but that you can never improve the city. "So you want a granary so you can eat? Sorry, I have to build another tank instead. Maybe next time."