Answer:
Bram Stoker had an affinity for the United States.
This is probably because Henry Irvin, his boss and for whom he was secretary for a long time, was popular there.
When Irvin was alive, he had along with him, been invited twice to the White House and was familiar with the then president of the United States of America. Records have it that two of Brams novels are set in America with Americans as characters.
Some analysts also speculate, given his expressions in Dracula, that he was a sexually repressed author perhaps due to his highly conservative background and that one of the reasons he loved America is that it gave him the liberty to be who he really was.
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