Why Poland? Poland was a nation for a short spell (reasonably powerful too) in the Middle Ages, then was basically absorbed by Russia and Germany, and only emerged again after WWI and then again after WWII, although it was only a satellite until the fall of Communism.
Also, Italians and Portuguese weren't really influential enough to really count as a civ.
Poland was powerful not only in middle ages but also in Renaissance until 18th century. Poland was under russian or german control totally for about 150 years in its 1050 years long history. Anyway Russia and Germany also were occupied some time (Russia was over 100 years under mongol domination.)
I wonder that you say nothing about Dutch or Vikings when questioning Portugese and Italians.
First were great first medieval explorers, and colonized America together with Spanish. They found Brasil, which is quite a big country now.
About Italians, they begun the Renaissance, and there were also Venetians and Genoans among them
(like Columbus).
Iroquis might have some cities, but they were still on neolitical level technically. I may be wrong, but they probably didn't have most of first civ advances like iron working or Wheel. Anyway, if they were the most advanced nation in North America i suppose we can add them to list:
Celts,vikings, portuguese, spanish, dutch?, italians, polish, turks, arabs, byzantines, ethiopians, mongol, korean, maybe thai?,incas, mayans, iroquis.