Greece was a major empire because had a lot of trading because of it's islands, and it had olives that were used for a lot of things like cooking, lamp oil, perfume etc.
The greek's downfall was the romans taking over and civil war for power.
rome grew because of it's military plans and strategies.
it's decline was because of the punic wars, both hannibal and the romans burned crops so the other would starve. this led to the farmers going broke, and the rich buying goods from elsewhere and the merchants going broke. and eventually this led to less and less money among the romans and the rest is history.