Roger didn't conquer shit
Roger never cared about territory
Roger was simply " Free ", free from anything, nothing could tell him what to do and what not, but in order for him to reach that level, he had to face all those who wanted to stop his ambition, and after many epic fights and adventures, he reached the top which allowed him to finally become " Free "
Roger's whole life turned about the idea of freedom, if I have to give Roger any description, I wouldn't say he's a revolutionary, not like Dragon, what he does is just weakning the WG in a careful way, something that Roger lacks, he wasn't careful at all, he faced whatever danger ahead of him. Roger had ideals, and had strength too, and his death gave birth to something that Dragon cannot pull (from what've seen from his so far)
I think in order to understand Roger, we need to go back to the very core of OP : Dreams, freedom, and Oda in Luffy's flashbacks reminded us very well of those two concept, especially when Ace was talking with Luffy at that cliff after Sabo's death (I don't believe he's dead btw)