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1.
First Europeans visit the U.S.
2.
First permanent European settlement on the U.S. mainland
3.
New Amsterdam becomes New York
4.
The last of the original 13 colonies is founded
5.
The Mason-Dixon line is drawn
6.
The first Treaty of Paris involving the U.S. is signed
7.
The first contested U.S. presidential election
8.
The 25th state is admitted
9.
The last law making property ownership a requirement for voting is repealed
10.
"A Visit from St. Nicholas" (aka 'Twas the Night Before Christmas) is first published
11.
The first transcontinental railroad is completed
12.
The Adventures of Huckleberry Finn is published
13.
Plessy v. Ferguson establishes the legality of "separate but equal" racial segregation
14.
The first U.S. Nobel Prize winner
15.
The last of the "lower 48" states is admitted
16.
The last significant (at least 100 square kilometers) U.S. permanent territorial acquisition
17.
The majority of the U.S. population is urban for the first time
18.
U.S. population surpasses 100,000,000 for the first time
20.
ARPANET (an important precursor to the modern Internet) is established