(NOTE:   In order to have as few historical time periods as possible, I altered history a bit, as you may have noticed by this list.   Also, many of these periods are either interchangeable or perhaps the line between them is fuzzy.  So if you are interested in a particular time period, try several searches with related key words -- Civil War, Riverboat, or Frontier, for example -- to find the books you are seeking.)

Prehistoric	ancient, ancient pre-history.
Egypt	ancient Egypt.
Greece	ancient Greece.
Rome	ancient Rome, Roman occupation.
Judea	ancient Judea, The Holy Land.
Celtic	Dark Ages, end-Roman to early Medieval (also pre-Roman Druid or Pagan).
Viking	.
Sheik	includes Sultan, Pasha, Harem (contemporary Sheikhs, too).
Medieval	through end-Henry VIII -- England and world.
Renaissance	Elizabethan through end-Stuart   (earlier in Italy).
Outlaw	includes Fugitive, Highwayman, Raider, Smuggler, Pickpocket, Robin Hood, Zorro.
Pirate	includes Privateer, Sea Captain   (if onboard ship).
Georgian	early-1700s up to 1799 -- includes America and world.
Colonial	America, before American Revolution.
American Rev.	American Revolutionary War.
French Rev.	France during the French Revolution.
Regency	1800 through mid-1830s -- includes America and world. (NOTE:   "Regency" is used here as a time period, not as a type of book.   Therefore, it includes both small "Regencies" and larger "Historicals" set during the time of the English Regency.)
War 1812	American War of 1812, war is mentioned.
Old South	Antebellum American South, before Civil War, plantation.
Civil War	American Civil War, war is mentioned.
Riverboat	Mississippi, Amazon, or any other river or canal.
Victorian	from mid-1830s to 1895 -- includes America and world. (NOTE:   Because the "Victorian" era covered so many years, I've moved the late-Victorian time period into the Edwardian. In BYRON, the years 1895 to 1901 is considered Edwardian.)
Frontier	includes Indians, Colonial Frontier, Wild West, Gold Rush, Mexico, Australia, Canada, Yukon.
Edwardian	late-Victorian, turn-of-last-century, 1895 to 1919, through World War I.
WW1	World War I, war is mentioned.
Russian Rev.	Russia during the Russian Revolution.
Chinese Rev.	China during the Chinese Revolution.
1920s, 30s	The 1920s and/or 1930s.
WW2	World War II, war is mentioned.
1940s, 50s	The 1940s and/or 1950s.
Korean War	Korean War, war is mentioned.
1960s, 70s	The 1960s and/or 1970s.
Vietnam War	Vietnam War, war is mentioned.
Cold War	.
Near Future	21st to 22nd centuries.
Far Future	beyond . . .