Polygamy was the norm for most of ancient/imperial China, Ottoman Empire, Mongols, Ancient Jews etc.
I wouldn't go so far as to say it was the norm for most people at most points in history, but considering the populations of the above civilisations it wasn't uncommon either.
FWIW, in ancient China people strictly only have one wife in most cases. The others are called concubines (I think). They have very different social/legal status.
I wouldn't go so far as to say it was the norm for most people at most points in history, but considering the populations of the above civilisations it wasn't uncommon either.