Yes, but they didn't decimate them, otherwise there would be none of them today... They colonized them, big difference. With colonization you bring in school/institutions, administrations, stuffs like that, just like the romans, it's wasn't war for the sake of total anahilation, there was that idea of control and development of the region, under roman rule. You can't do everything at gun point, it's one thing to take a position, it's another to maintain yourself over there for centuries, and to achieve the latter you need to bring in something that creates a consensus around the fact that yes you're yet another invader/gang if you will, BUT with you, everybody gets a meal, trains arrive on time etc, so it's a win win if you will. That's how roman conquest worked for the most part and why colonization worked also, because the colonizers brought with them a social order/organization where most had the opportunity to win something It's starwars also it's a bit like that with the empire, they're bad but a lot of people work for them because at least with the empire you get autobahns electricity and tap water, it's not all bad Successful gangs/criminal organization also rely on the fact that many locals rely on them to bring food on the table, they're bad BUT... They deliver...