Era
20th century
78
19th century
53
1564-1616
28
18th century
20
Revolution, 1775-1783
17
Colonial period, ca. 1600-1775
12
17th century
11
Civil War, 1861-1865
11
1724-1804
10
Pennsylvanian
10
1819-1880
8
1882-1941
8
21st century
8
Devonian
8
1945-
7
2001
7
1622-1673
6
1703-1791
6
1809-1892
6
1897-1962
6
1917-1963
6
1960-
6
Cretaceous
6
16th century
5
1770-1831
5
1812-1870
5
1812-1889
5
1818-1883
5
1859-1952
5
1886-1968
5
1888-1953
5
1906-
5
1933-1945
5
1946-
5
1947-
5
1949-
5
1225?-1274
4
1509-1564
4
1593-1633
4
1596-1650
4
1741-1803
4
1775-1865
4
1800-1899
4
1804-1864
4
1819-1891
4
1844-1900
4
1850-1904
4
1867-1933
4
1869-1935
4
1879-1970
4
more ...