The only exchanges that matter are GDAX, Bitfinex, Gemini and Bitstamp. All foreign trading volumes do contribute somewhat, but they mainly affect their own market. I remember when South Korean exchanges were trading $5000 above western exchanges, which is beyond insane, but the western markets didn't give one single damn. Later on South Korean premiums vanished and became just a few hundred instead of thousands -- this perfectly indicates that continents have different demand standards and don't necessarily steer the other side up or down with it. That's the benefit of having different exchanges all operating different order books. 
The price discrepancies between exchanges have more to do with peculiarities and issues like withdrawal and deposit fees on fiat transfers rather than "continents having different demand standards". If everyone were able to both flawlessly withdraw and deposit fiat (and sometimes crypto as was the issue with Chinese exchanges in the first half of 2017), the arbitrageurs would quickly jump at the opportunity to make easy money and level out prices. If there were equal conditions at every exchange out there, the prices would be pretty much the same everywhere in the neighborhood. Things like withdrawal and deposit fees, limits on withdrawal amounts, times to withdraw and deposit, etc explain such big differences in prices on various exchanges.