Possibly the telegraph. Morse code came into place with that. People could communicate with ticks.
I'd think that one advantage of nationalism is the unity it builds among people who share the same nation, who start to think of each other as co-citizens.
One disadvantage of nationalism is the hate can be directed against outsiders.
Johannes Gutenberg was most commonly associated with the printing press.
The Louisiana Purchase<span> (1803) was a land deal between the </span>United States<span> and France, in which the </span>U.S. acquired<span> approximately 827,000 square miles of land west of the Mississippi River for $15 million.</span>
