U. S. Unemployment Rates

What was going on in the world at the time of these unemployment rates? How many people who want to work should be out of work? Am I my brother's keeper?

1916: 5.1%
1926: 1.8%
1936: 16.9%
1946: 3.9%
1956: 4.4%
1966: 4.5%
1976: 7.7%
1986: 7.0%
1996: 5.4%
1006: 1.7%