Okay seems to be a universally recognized expression across the globe. What's it first recorded use and where does it come from? Was it British or American influence that spread the word globally?
Honestly, no one knows. The wikipedia article gives a good primer on the possibilities, but there really is no consensus on the definitive etymology. I could attempt to elaborate on the pros and cons of every possibility, but having taken classes that touched on it and having looked into the matter myself extensively, the wikipedia article really gives you everything you need to know: http://en.wikipedia.org/wiki/Okay.