Era
Quaternary
21
Cretaceous
18
Precambrian
11
Pre-Quaternary
9
Eocene
8
Paleozoic
7
Civil War, 1861-1865
6
Tertiary
6
Pennsylvanian
5
20th century
4
Mesozoic
4
Cenozoic
3
Jurassic
3
Partition, 1995
3
Permian
3
Silurian
3
1945-
2
1979
2
1979-
2
19th century
2
Ordovician
2
Paleocene
2
1596-1673
1
1770-1838
1
1774-1809
1
17th century
1
1815-1871
1
1862-1877
1
1866-1895
1
1871-1918
1
1913
1
1918-1945
1
1930-2006
1
1933-1945
1
1945-1989
1
1945-1992
1
1947-
1
1960-1988
1
1961-
1
1962-
1
1963
1
1965-1980
1
1970
1
1970-1973
1
1971
1
1990
1
2012
1
800-1444
1
Cambrian
1
Devonian
1
more ...