What does john adams mean when he called the constitution "the greatest single effort of national deliberation that the world has ever seen"

That was exactly what he meant - he considered the Constitution to be a perfect document which would cater to everyone's needs. He believed it was a perfect example of democracy and thought it would bring a bright future to America. He had absolute trust in it when it was drafted, which is why he said that quote.

Well since there aren't any choices i dont know if this is right but nationalism played an important role in the unification of both italy and germany i do believe