The Americans founded this island city far away from their capital, but near to the french homeland. It seems they wanted to prevent a flip by building this city out of the radius of Cherbourg.
The spot 1 NE looks much better, at least they could have 2 shields in the future
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To tell from my games, the AI is usually not too shy to build in my radius. So does the AI take the possible flip in account?
(IIRC only a city you share some radius with can flip to your side)