I don't know if they still do this, but it used to be America was NTSC and only NTSC games would play on the American consoles and UK was PAL.
Here is a color picture: http://en.wikipedia.org/wiki/File: PAL-NTSC-SECAM.svg
^^^ delete the space between "file" and "pal", I had to add a space else it would make a smile sticking his tongue out.