How did each of the great world empires fall?

Question

Roman? Egyptian? British? Russian? Mongol? Italian?

and any other

Answer 1

The empires overextend themselves.  Maintaining empire is costly and not in the country's best interest.  Alexander the Great had a vast and sprawling empire but he had no heir to inherit it so it was carved up by his generals.  

The Period of Decolonization was also a result of the weakened nations unable to maintain their empires due to the costly war.  

Answer 2

Italian Empire ????????

Anyways, it seems each country does well enough economically, got a system that works all right, then they develop their military and try to expand and maintain their expansion.That last bit of pride and ambition ALWAYS ends up with collapse of their Empire.  Their conquered territories eventually feel used and abused, and fight for their freedom and self-determination back, and the costs of trying to prop up the over-expanded empire becomes overwhelming, no point to keep it going.  The territories / colonies revolt.  The empires shrink or fail outright.

Answer 3

you forgot one

the American Empire

Im writing a book as we speak "Empire Destroyed: Fall of an American Dream"