Pre WWII
~1941.The Great War or earlier
World War II
1941-1945, The Greatest War on the earth ever.
Post WWII
1945-1960, mainly Korean War
The Vietnam War
1960-1975, Second Indochina war
Post Vietnam War
1975-2000. Operation URGENT FURY, Operation JUST CAUSE, Operation DESERT STORM, Operation GOTHIC SERPENT, etc.
Modern Warfare
2000-2010. Operation IRAQ FREEDOM, Operation ENDURANCE FREEDOM, Global War On Terror.
Post GWOT
2010-now.