My first guess is because they were attacked by foreign invaders.
(but at the same time, both empires had split in their own way. The Han empire lost control and broke into different areas. The Roman Empire had become two parts, where the Western part was constantly attacked by Germanic tribes). Both sides were constantly attacked by invaders until there was no more land to take.
The ancient Chinese have invented many things that have a huge impact in today’s society. They created paper, kites, silk, compasses, porcelain, the wheelbarrow, gunpowder, and tea production.
Mussolini's government has really changed the country, and Italy took part in the first world war. In 1920s there were also climate changes.
Some countries did not like the countries we were with an alliance with, so they would attack them and we would attack the country who did it, and so on.
