[zaarn]

Years in which the US was not at war:

- 1796 and 1797

- 1807, 1808 and 1809

- 1826

- 1828, 1829 and 1830

- 1897

- 1935, 1936, 1937, 1938, 1939 and 1940

- 1976, 1977 and 1978

- 1997

- 2000

This list counts major wars until 2016. Some of the wars led in this time were of defensive nature. This list does not account for covert operations and other, similar acts that might be considered war.

[alex_young]

Since 1955: The Korean war was never ended, and there was an active and continued military engagement with daily exchanges in Iraq from 1991 through 2003.

The mainland United States has not been attacked as a part of a military operation in the modern era, so the defensive claim is questionable.

[zaarn]

I pulled the list from the internet, it was probably incomplete. I sadly can't amend it anymore. The defensive claim is from the source I used.