Actually I find most of the advice here inaccurate. Dwarf hamsters and especially robos are quite social in the wild and should be kept in groups (clans) if possible. We've had dozens of campbell's dwarf in the same cage and 8 adult robos with I don't know how many pups at one point.
However there are a million things you can do wrong to cause their quite normal arguments (even if they get rather loud it's just the loser saying they lost) to turn in to bloody ones instead. Females are the worst to try to keep a group of when it comes to rodents because they control the breeding and hierarchy. Males make clans much easier and larger because they don't care as much about territory for their young and breeding rights so they are less concerned about who is above who. Female only clans are best kept in no more than a trio with a specifically designed cage, resource setup, size (too big can actually cause problems the same as too small), cautious adding of objects that could be claimed, etc... In the end most can't pick up on the subtle cues of why their hamsters are arguing and are best just keeping them separate even if the hamsters evolved to be social animals and have a clan to sleep and forage with.
Kind of like our rabbits are social but territorial so we can make colonies but we have to break the rules generally followed in rabbit keeping such as when it comes to size allotted per rabbit as well as pay attention to personalities, overall size of pen, layout-objects to break things up and food/water/other resources not in a place that can be claimed, nesting situations.... Some people just can't or don't want to observe enough or do the work so they prefer or have to use individual cages. Same concept but on a much smaller scale with hamsters, gerbils, and their relatives which I've had a few uncommon ones like duprasi.