Paul was a member of the Jewish Diaspora, and the people of Jerusalem knew him only by reputation, not by face.
Paul and the leadership at Jerusalem (James, Cephas and John) were at loggerheads with one another. That is the reason they fought him; Paul had a "no-Law" Gospel but the Jewish Christians from Jerusalem demanded full obedience to Mosaic traditions and laws, signified through male circumcision.
When they spoke about "all nations", they knew of the nations around the Mediterranean (meaning "middle of the earth") plus those nations involved with trade (India, etc). And Paul wrote that the Gospel (his version of it, anyway) had reached all nations. He and the rest fully expected the "end" (Coming) to take place within their own lifetime.
There is absolutely no way that one can relate the nations that we know with the nations which existed in their times. Even modern nations such as Italy, Germany, and Iraq are very recent federations of disparate states. And to think that Paul (or Daniel or the Revelator) knew anything about USA, Russia and so on is beyond belief.
Doug