I have no problem with it being in the game, indeed it should be an emergent faction. The fact that it is playable is extremely odd however given that there are only 12 playable factions. Consider, in 1700 Portugal was a world power, had an overseas Empire to rival most other factions, and was a strong naval and trading presence. And the US... didn't exist.
I think the decision to make them playable was probably motivated by a desire to reach out to the American market.
I wouldn't mind that the US was playable at all if Portugal was as well, or if CA had gone with a greater number of playable factions. It's just that they grabbed quite a coveted spot away from a nation which more than deserves it.
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