royalsociety.org/grants-schemes-awards/awards/copley-medal/ says it is now open to international citizens, but having a quick look at the 2010 awards still suggests that it is very British centric, or at least anglophone centric, much like the society fellowship itself. That's likely the reason why the Nobel prize won, being much more international from the start.
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The Copley Medal is one of the most prestigious awards in the field of scientific research. It is awarded by the Royal Society of London, which is one of the oldest scientific academies in the world. Established in 1731 by grants from the society's founding member, Sir Godfrey Copley, the medal is given for outstanding achievements in scientific research in any branch of science.