Center & Centre
Why do the British and North Americans spell the same words differently?
I don't know why it originally started, but the Americans spell things as they sound, whereas the Brits have had influence from many invasions, mainly the French, and many of our words have derived from that.
Rather off topic but, I find it many times writing on this forum, and have found that I now automatically spell it the US way, so would probably spell words instantly wrong if I were writing a letter!
The main 'offenders' that I find are color and neighbor (as opposed to our colour and neighbour!)