[Not a Bug] New focus city?

[Dutch Airways]

I'm in world 6, currently I have a terminal in Amsterdam and hong-kong is a focus city.

I thought; I want to go to the america's and set-up a focus city in Mexico City, rented my five gates and then I coudn't made a focus city  

how come this is not possible ? I made Hong Kong a focus city why can't I make Mexico City a focus city ?

[StephenM]

World 6 only allows one Foreign Base/Focus City.

[zkvac]

Also you only need 4 gates, not 5.