Fire Emblem Fates is split into three story paths. Conquest is one of the two base stories, the other being Birthright. The other story path can be bought digitally at a discount through the in-game store. The third story path is Revelation, a DLC that was released later. You need to be have completed Chapter 6 in either game to access the other stories and DLC. Conquest is the hardest of the three paths, having reduced ability to grind experience from maps, tougher mission objectives, and giving less money and experience for those missions.