Apostrophe has two major functions each of which has its own peculiarity.When a pronoun takes Apostrophe it betokens abbreviation but when a noun takes it, possession is depicted...eg..the book is Mike's/My father' etc(possession)...He's home(abbreviation..He is...)
"America" is a noun,a proper one for that matter,therefore it can take Apostophe to show ownership.However,there is a little problem here which has to do with whether America can be said to own the manager.
I would have wanted to say "American manager" but for the fact that a non-American can become manager in America and even of America.
To this end,if I may suggest,I think it'll be safer to say something like this..."the manager of America"...because he uses his managerial expertise to the advantage of America.Therefore,as a matter of peroration,I wish to conclude that since a nation cannot be said to own or possess her inhabitants,it may be loose to have expressions like "America's manager"
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