Buffs (green) or Debuffs (red) are displayed directly above your units. I don't want to go into all of them here, but rather draw your attention to them. In particular, if you are flanked (2nd symbol from the right), you will receive a permanent penalty on your morale. I gather from the symbol that I am flanked from the left. The icon also turns green when my left flank is protected by allies.

If your morale drops below 0, the unit will flee. Unfortunately not always in the right direction, so you can steer in the opposite direction. As long as the unit is still in contact with the enemy under a complete loss of morale, the morale bar sinks further into the negative and also takes longer for it to regenerate.

If your unit loses too much manpower and thus also life points, the visibility and morale of the respective unit will also be reduced to an absolute minimum. Being flanked once means the elimination of your unit.

The second key factor is the terrain on which you move. In particular, the forest as a red symbol should make you think. Almost all units of all factions get worse bonuses when fighting in the forest. The only exceptions here are the entire barbarian faction and individual Carthaginian mercenary units, which even receive a buff here.