Infantry could cause fear in rtw, dont see why it would have been dropped. Its not something that can be added by a trait though, the effects traits can have are hardcoded and theres not many of them, heres the list ripped from the exe:
Combat_V_Religion_
Combat_V_Faction_
BattleSurgery
TrainingAnimalUnits
HitPoints
BodyguardValour
Looting
Law
Unrest
Squalor
ArtilleryCommand
GunpowderCommand
InfantryCommand
CavalryCommand
Fertility
TaxCollection
Mining
Farming
FootInTheDoor
LocalPopularity
Trading
Construction
TrainingAgents
TrainingUnits
LineOfSight
Electability
BribeResistance
Bribery
PublicSecurity
PersonalSecurity
NightBattle
SiegeEngineering
NavalCommand
Ambush
SiegeDefence
SiegeAttack
Defence
MovementPoints
TroopMorale
Loyalty
Subterfuge
Management
BodyguardSize
Generosity
Boldness
Disposition
Violence
Purity
Eligibility
Sabotage
Assassination
Authority
HeresyImmunity
Unorthodoxy
Piety
Finance
Charm
Influence
Command