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It isn't so much about timezones for me, its more about which servers get played on. There would be one continent where battles are always on NA servers, and the other always on EU servers. If you wanted to cover timezones you would see need EU clans, but they would suffer because of ping. EU clans will never be offensive against NA clans and vicesa versa, simply because the defender gets to choose which sever to play on. Leading to huge power blocs and stalemates.
And well fuck port cities then, you can simply walk across the water now as it is. It would look a little weird if armies met and fought on the ocean, but manageable. Water isnt a barrier at the moment, neither are mountains.