Pre WWII
~1941.The Great War or earlier
World War II
1941-1945, The Greatest War on the earth ever.
Post WWII
1945-1960, Korean War
The Vietnam War
1960-1975, Second Indochina war
Post Vietnam War
1975-2000. Operation Urgent Fury, Operation Justice Cause, Operation Desert Storm, Operation Gothic Serpent
Modern Warfare
2000-now. Operation Endurance Freedom, The war against terrorism