Nothing spectacular happens after turn 225 you can continue as is, or start over again. Most factions are at the pinacle of their technology by the time the new world is discovered although if you keep playing eventually the AI starts sending hi-tech decent troops your way (scots gaurd handgunners musketeers late hvy cav etc) which makes it kinda interesting. I prefer the late to early game so as i oft post,most of my games have exceeded the 225 mark already.