The collapse of the USSR

The seeds were there near the beginning. A couple of leaders were positing maintaining private agriculture back in 1928-29. Stalin said no, even if it possibly meant civil war. Eventually, the burgeoning urban population strained already plummeted grain productivity. Oil revenues could buy food for a while, until the Saudis decided to stop propping up oil's price. The article makes a parallel with the Spanish empire when mentioning establishment of empires on unstable resources:

The Spanish empire, without losing a single battle on the ground for fifty years, managed to lose all of its possessions in Europe outside of the Pyrenees...

Link to whole article here.