The greek world became a split up into large military empires. Alexander the great conquered the greek world, died and left it to his successors. The whole aim of that was to conquer, to er, take new worlds, as it were, into their sphere. So many such conditions led to what is seen as an efflorescence of ideas. And then you get these states like venice and dividual towns which can compete with each other for relative freedom in disseminating ideas. Of course there are some cultural questions about how this could be done - but i think they add up to create the conditions for innovation to flourish.