Morale States:

Impetuous: 10 and above
Steady: 2 to 14
Uncertain: -5 to 5
Wavering: -14 to -5
Routing: Less than -6

Rout point is -18 in MTW/VI for MP.
Routed units will keep routing until their morale rises to -6 or above.
Hitting the rally key pumps +8 morale into the unit.

Impetuous units will pursue enemies for longer, and may disregard orders to hold position. #Some troop types may charge without orders.

Uncertain or wavering units which are not fighting are less likely to charge, and those who are fighting are more likely to fall back.

Negative Morale Effects:

Loose or disordered formation: -2
Outnumbered 2 to 1: up to -4 (range = about 75 meters)
Outnumbered 10 to 1: up to -12 (range = about 75 meters)
Outclassed in quality and speed: modifies the outnumbered penalty.
One flank threatened: -2 (range = about 60 meters)
Two flanks threatened: -6 (range = about 60 meters
Charged in flank: -4
Infantry charged by cavalry in flank or while disordered: -6
Charged in flank by unit hidden in forest: -8
General's death (for first few seconds): -8 to all his units except highly disciplined units
General's death (after first few seconds): -2 to all his units except highly disciplined units
Routing Friends: up to -12 for seeing 2 equal or higher level friendly units routing. #Elite and disciplined units consider lesser types as 1/2 a unit for this calculation.
10% of unit is dead: -2
50% of unit is dead: -8
80% of unit is dead: -12
Taking casualties from enemy missle fire: -2 for a duration less than the reload of the firing unit (additional -4 for gunpowder weapons)
Unit is very tired: -2
Unit is exhausted: -6
Unit is totally exhausted: -8
Losing: Up to -8 (up to -14 if losing to cavalry)
Skirmishing without ammo: -6
Skirmisher pursued for a long distance by equal speed unit: -6

Positive Morale Effects:

Two flanks protected: +4
No retreat possible (usually castle sieges): +8
No enemies around: +4
Two enemies routing: up to +8
Uphill Position: +2
Winning: up to +6
Unordered charge: +4 (such as when impetuous knights charge automatically)
Outnumber Enemy 3 to 1: +4
General's unit: +2
Within 50 meters of general: +1 morale per command star
Beyond 50 meters from general: +1 morale per 2 command stars