Letter	Number	Sub heading
A		American History by topic
	1	Bibliographies
	2	Reference works
	4	Primary sources
	5	General textbooks
	6	Miscellaneous collected essays
	7	Miscellaneous monographs
	8	Historiography
	100	Political and constitutional history
	200	Diplomatic history
	300	Economic history
	400	Social and cultural history
	500	Intellectual history
	600	Regional history and historical geography
	700	Biography and memoirs
B - R		American History by period
	1 - 700	(as A 1 - 700)
B		Early history to 1607
C		Colonial history, 1607 - 1763
D		American revolution and confederation, 1763 - 1789
E		The early national period, 1789 - 1815
F		Nationalism and sectionalism, 1815 - 1848
G		Sectional conflict, 1848 - 1861
H		Civil war, 1861 - 1865
HB		The confederacy, 1861 - 1865
J		Reconstruction, 1865 - 1877
K		The gilded age, 1877 - 1901
L		Progressive period, 1901 - 1921
M		Interwar period, 1921 - 1939
N		World war II, 1939 - 1945
P		Cold war period, 1945 - 1976
R		Detente, 1976 -