The American novelist was, in fact, famous earlier and much better known that his British counterpart; his novel Richard Carvel (1899) sold around two million copies. Later novels, The Crisis (1901) and The Crossing (1904) were also very popular. The two are still occasionally confused, mostly by sellers of second-hand books (having ‘Churchill’ as the author of books with similar titles – The Crisis and The World Crisis – doesn’t help).
Interestingly, both Churchills shared a lot in common; both had political careers, both were noted amateur painters, both attended military colleges and served (during the same period) as officers in the armed forces (the American Churchill was in the navy).
Churchill, on learning of the American Churchill’s books, wrote to him suggesting that he would sign his own works “Winston S. Churchill”, using his middle name (actually part of his full surname, ‘Spencer-Churchill’) to differentiate them. This suggestion was accepted, with the comment that the American Churchill would have done the same, had he any middle names. The two actually met in Boston (the meeting made the front page of the Boston Herald).