I'm creating an antiquity-age earthlike world starting at the early bronze age. One of my continental interiors is a large, fairly flat, hot steppe region predominantly covered in steppe woodland, situated between 15 and 30 degrees latitude. With my research, I've come to the idea of this being like a warmer version of the Ukrainian forest steppe, though I may be wrong. Through this grassland region is a large navigable river system, annually flooded by glacial melt in neighboring mountains, carving a river valley into the land. In my head, this seems like a great place for a river valley civilization, but I know that large grassland expanses are more suited to nomadic pastoralists. The river flows south, leaving this region and entering a deciduous forest, then the equatorial lowland jungle before reaching the ocean.
Is a region like this suitable for a river valley civilization? If not, what aspects make in unsuitable, and if so, what challenges might this civilization face?