Era
20th century
67
19th century
58
1775-1865
48
Civil War, 1861-1865
26
1951-
24
1865-1950
17
1865-
14
Colonial period, ca. 1600-1775
14
1865-1877
13
1897-1962
12
1865-1951
9
Revolution, 1775-1783
8
18th century
6
1890-1980
5
1783-1865
4
1857-1861
4
Tertiary
4
1863-1877
3
1911-1983
3
Cretaceous
3
Ordovician
3
To 1775
3
16th century
2
1789-1869
2
1806-1870
2
1807-1870
2
1815-1861
2
1835-1910
2
1865-1900
2
1865-1933
2
1873-1945
2
1877-1934
2
1897-1966
2
1905-1989
2
1909-2001
2
1917-1967
2
1918-
2
1924-
2
1929
2
1945-1989
2
1989-
2
21st century
2
Eocene
2
Miocene
2
To 1863
2
approximately 1500-1542
2
-1855
1
1564-1616
1
1718-1779
1
1739-1823
1
more ...