"Periodicization" is a source of never-ending strife among historians. The vehemence of such debates points to an important truth: the way we define periods in the past has a significant bearing on the way we think about history. To see that this is the case, one need only recall the moniker "The Dark Ages" and all that it implies.
For the purposes of this site, periods are broken down according to longstanding and common conventions in American history. Doing so does not imply that these periods cannot be challenged, or even that some of them are entirely tenable. But every historian must demarcate periods in some way in order to make sense of the past.
The era names used on this site correspond to the following periods:
Colonial: From Spanish colonization of Florida and the southwest to the beginning of the Revolution (16th century to 1774)
Revolution and New Republic: From the first shots of the Revolution to the end of Thomas Jefferson's second term (1775–1808)
Antebellum: From the presidency of James Madison to the beginning of the Civil War (1809 to 1860)
Civil War and Reconstruction: From the beginning of the Civil War to the end of the federal government's active reconstruction of the South (1860 to 1876)
Late 19th Century: From the end of Reconstruction to the turn of the twentieth century (1876 to 1899)
Progressive Era: From the beginning of the twentieth century to the stock market crash (1900 to 1929)
Great Depression and World War II: From the beginning of the depression to the end of the war (1929 to 1945)
Post-War 20th Century: From the end of World War II to the turn of the 21st century (1945 to 1999)