Columbia subject headings:
Russia--History--1801-1917--Mathematical models.
Russia--History--20th century--Mathematical models.
United States--History--20th century--Mathematical models.
United States--History--Civil War, 1861-1865--Mathematical models.
Harvard subject headings:
Russia--History--1801-1917--Mathematical models.
Soviet Union--History--1917-1936--Mathematical models.
United States--History--1865-1921--Mathematical models.
United States--History--19th century--Mathematical models.
United States--History--20th century--Mathematical models.
Princeton subject headings:
History--Mathematical models.
Russia--History--19th century--Mathematical models.
Russia--History--20th century--Mathematical models.
United States--History--19th century--Mathematical models.
United States--History--20th century--Mathematical models.