Era
1945-
8
20th century
7
20th century --
4
19th century
3
Congresses
3
1945 -
2
1950-
2
1960-1980
2
1980-
2
1981-
2
Congresses --
2
1478-1798
1
1789-1900
1
1800-1837
1
1801-1917 - Sources
1
1869 - 1948 -- Political and social views
1
1900-
1
1943
1
1945 - 1970
1
1945-1989
1
1946-
1
1950-1953 --
1
1951-1979
1
1955-1983
1
1959-
1
1960
1
1960-
1
1966-
1
1970 -
1
1971-1981
1
1975
1
1976 -
1
1982
1
1985-1991
1
1985-1995
1
1990-
1
20th century - periodicals
1
20th century-periodicals
1
20th century. --
1
Alexander II, 1855-1881 --
1
Case studies 3
1
Methodology
1
Modern period, 1600-
1
United States
1
economic condition
1
handbooks, manuals, etc
1
social aspects
1