If your question is about major wars from all over the world:
Not sure how far back you want to go, but it is wise to start with European history wars leading to modern history. You may begin with the Hundred Year Wars between England and France (1337 to 1453).
Skip to the Franco-Indian War (French Indian) of 1754 to 1763, and the Seven Year's war (1756-1763) and move on to the American Revolution of 1776 which set the foundation to the United States Then I would move on to the War of 1812, which lasted until 1816. Then there is the Spanish American war in 1898 where plenty of Spanish colonies became U.S territories.
If what you are referring to are the WW's, then:
World War I was from 1914-1918, while World War II was from 1939 to 1945. There has not been a WWIII yet (thank goodness).
Other major world conflicts were:
The Korean War, which was from 1950-1953 and the VietNam War that lasted from 1965-1975.
The latest most resounding wars from around the world are:
- Iran Iraq that lasted from 1980 to 1988
- Persian Gulf war in 1991
- and the War on Terrorism (Post Sept 11) which started in 2001 and has taken different names, tactics, and degrees of engagement as the Presidencies have changed.
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