Its a long story. The correct understanding should be that Qin conquered the 6/7 warring states (near and around the Yellow River) and became the first emperor of Qin Dynasty (about 200BC). Few hundreds years later this became Han Dynasty, so the ppl are referred to as Han tribe (or Han Chinese), the next many hundred years Hans fought against many other tribes, Tibetians, Mongols, Manchus, etc, eventually Manchus conquered everyone and became Qing Dynasty.
Seriously speaking, Chinese is still spilt today (mainland China, Taiwan, Mongolia).