Short answer to the question: Aren't most Quakers in America?
Very short answer: No.
Quakers set out from England to the new world in the very early days of
the society, and for about 300 years there were more Quakers in north
America (the USA after independence) than in Britain. (More about the
history
here.)
But following missionary outreach from the USA to other countries there
are now far more Quakers outside Europe and the USA, especially in
Africa (mostly in Kenya).
Many more details, and lots of numbers, are shown
here in the answer about how many Quakers
there are.
A comprehensive and informative website covering Quakers in the USA
is here.
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