List, from least to most severe:
DEFCON 5: Peacetime. No threat to 1980s America.
DEFCON 4: Increase regional alertness to above peacetime (normal) levels. Spies/infiltrators have been uncovered.
DEFCON 3: Mobilize armed forces to above normal readiness. Invasion has been suspected.
DEFCON 2: Raise armed forces readiness to just below maximum. Invasion and/or war is imminent.
DEFCON 1: Region is being invaded or is at war. Armed forces are to be brought to maximum readiness and are to be mobilized against invading force(s).