How did Rome go from being one of the most impressive empires ever to Italy being a 3rd rate military power?

We've evolved as a society; at some point you're no longer a youngster and you leave those trivial things like being the world's top military power to the little ones oversea. Similarly, will you still care about having the largest Hot Wheels collection when you're 20?

Meanwhile, we've focused on those aspects more appropriate for an adult civilization, such as being the world's first (and undisputed) spaghetti power 🍝