By the 4th century BCE, Rome started to incorporate its neighbors, like the Latins and the Etruscans, and pretty soon they had all of Italy under their control. But that's not really diversity of subject peoples. I mean, nothing personal, Italians, but you know, you have a lot of things in common, like the constant gesticulations. If you want to talk about real expansion and diversity, you've got to talk about the Punic Wars. These were the wars that I remember primarily because they involved Hannibal crossing the Alps with freaking war elephants, which was probably the last time that the elephants could have risen up and formed their awesome secret elephant society with elephant planes and elephant cars. In the first Punic War, Rome wanted Sicily, which was controlled by the Carthaginians. Rome won, which made Carthage cranky, so they started the second Punic War.