The History of the United States
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History of the U.S.
Pre-Columbian Era

Colonial America (1492-1763)

Revolutionary Period (1764-1789)

The New Nation (1790-1828)

Western Expansion & Reform (1829-1859)

Civil War (1860-1865)

Reconstruction (1866-1877)

Gilded Age (1878-1889)

Progressive Era (1890-1913)

Great War & Jazz Age (1914-1928)

Depression & WWII (1929-1945)

Modern Era (1946 - present)

State Histories


Prehistory of the United States

AlanThe prehistory of the United States comprises the happenings within regions now part of the United States of America during the interval of time spanning from the formation of the Earth to the documentation of local history in written form.  At the start of the Paleozoic era, what is now "North" America is actually in the southern hemisphere. 

Marine life flourishes in the country's many seas, although terrestrial life has not yet evolved.  During the latter part of the Paleozoic, seas are largely replaced by swamps home to amphibians and early reptiles.  When the continents have assembled into Pangaea drier conditions prevailed. The evolutionary precursors to mammals dominate the country until a mass extinction event ends their reign.

The Triassic, first period of the Mesozoic era follows.  Dinosaurs evolve and beg in their rise to dominance, quickly spreading into the United States.  Soon Pangaea begin to split up and North America began drifting north and westward.  During the latter Jurassic, the floodplains of the western states are home to dinosaurs like Allosaurus, Apatosaurus, and Stegosaurus.  During the Cretaceous, the Gulf of Mexico expands until it splits North America in half.  Plesiosaurs and mosasaurs swim in its waters.  Later into the period it begins to withdraw and the coastal plains of the western states are home to dinosaurs like Edmontosaurus, Triceratops, and Tyrannosaurus.  Another mass extinction ends the reign of the dinosaurs.

The Cenozoic era begins afterward.  The inland sea of the Cretaceous gradually vanishes and mammals are beginning to dominate the land.  During the Eocene the western states are home to small primitive camels and horses as well as the carnivorous creodonts. Soon mammals have entered the oceans and the early whale Basilosaurus swim the coastal waters of the southeast. Rhino-like titanotheres dominate Oligocene South Dakota.  From this point on the climate in the United States cools until the Pleistocene, when glaciers spread.  Saber-toothed cats, wooly mammoths, mastodons, and dire wolves roam the land. Humans arrive across a land bridge between Siberia and Alaska and may play a role in hunting these animals into extinction.


  • Precambrian

  • Paleozoic

  • Mesozoic

  • Cenozoic

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