I have often heard that the Qin dynasty was the first to unite China. For example, Wikipedia says:
Qin Shi Huang, or Shihuangdi, was the founder of the Qin dynasty, and first emperor of a unified China.
However, didn't the Western Zhou dynasty also unite China?
I understand that the Zhou dynasty kings slowly lost power, being reduced to a figurehead during the Eastern Zhou dynasty with real power fragmented into several states. However, many later dynasties also ended in fragmentation (e.g. the Han, Jin, and Tang dynasties), so I don't think this explains why the early Zhou dynasty isn't considered to have united China.