Rome wasn’t built in a day. It didn’t fall in a day, either. Rome lasted for hundreds of years after the ascension of Caesar and the fall of the Republic. They had to divide that sucker up and chop it into pieces before it finally went down. It was the Rasputin of empires.
Now, you get something as successful as that, and everyone thinks that that’s the natural order of things.
You get a great country. You have a bitchin’ army. Your people are filled with national pride and fervor. What’s a leader to do? (With apologies to Stan Lee.) Why, it’s Conquering Time.
The problem is those pesky other countries. They have this wacky idea that their country is, well, their country. The natives are inevitably difficult and whiny. What with the complaining that their homes and resources are being stolen. Crybabies.