I've been reading a lot about Medieval history recently. This is an experimental synthesis of my new understanding.
Early middle ages (800 - 1200)
Feedback loops (early)
graph TD A[Invading Armies] --> |Need for defense| K[Knights] K --> |Require wealth| F[Feudal relations] K --> |Carry armor| AW[Armor weight] AW --> |Selective breeding| HS[Horse strength] K --> |Ride| H[Horses] HS --> |Can carry more| AW HS --> |More power| DH[Draft Horses] H[Horses] --> |More available| DH DH --> |Faster than oxen| FY[Farm Yields] TFS[Popularity of Three Field System] --> |Better land use| FY[Farm Yields] TFS --> |Increased soil fertility| FY TFS --> |Popular winter crop| O[Oat Yields] O --> |Horses ♥ Oats| H AW --> |Unidentified horse and rider| Heraldry DH[Draft horses] --> |Used for transport| PM[Peasant mobility] PM --> |Cut out merchants| CT[Cheap transport] PM --> |Commute on horseback| TS[Town size] TS --> |City scale benefits| PP[Peasant prosperity] CT --> |Less spent on transport| FP[Farm profits] CT --> NF[Farm distance from rivers] NF --> |More food production| CC[Carrying capacity] FP --> PP CC --> PP FY[Farm Yields] --> PP PP[Peasant Prosperity] --> |Free time| LL[Lay literacy] LL --> |Personal interpretation of Bible| HER[Heretics]
Late middle ages (1200 - 1500)
Feedback loops (late)
graph TD AW[Armor weight] --> |Bolts could pierce| C[Crossbows] C --> |Too slow| L[Longbows] L --> PP[Peasant Prosperity] C --> |Attempt to prevent puncture| AW BD[Black Death] --> |Supply of workers decimated| HL[Human Labor Cost] HL --> |Economics| ML[Mechanical Labor] ML --> PP[Peasant Prosperity] HL --> |More profit| PP PP[Peasant Prosperity] --> |Uprisings| KW M[Mercenaries] --> |Need for control| SA SA[Standing Armies] --> RP[Royal Power] SA --> |Reduced need for knights| KW CAN[Cannons] --> |Castles obsolete| KW[Noble Weakness] L[Longbows] --> |Armor piercing| KW C[Crossbows] --> |Armor piercing| KW MUSK[Muskets] --> |Armor piercing| KW HL[Human Labor Cost] --> |Higher wages| KW CAN --> |Effective siege weapon| RP KW --> FD[Feudal decline]