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docs/systems/_index.md

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 Core mechanics that govern how the game economy and logistics work.
 
+## Expansion
+- [Settlement](./settlement.md) - Settling new islands and cities
+
 ## Trade & Logistics
+- [Trading](./trading.md) - Complete trading system overview (passive, active, contracts)
 - [Trade Routes](./trade-routes.md) - Automated ship loops between islands
 - [Diplomatic Trade](./diplomatic-trade.md) - Passive buy/sell with AI via treaties
 
+## Progression
+- [Accolades](./accolades.md) - Hall of Fame metaprogression and achievements
+
 ## Economy
 - [Maintenance Model](./maintenance.md) - Building upkeep and workforce costs
 - [Area Effects](./area-effects.md) - Proximity bonuses and penalties
 - [Statistics Screen](./statistics-screen.md) - Production vs consumption diagnostics
 
+## Resources
+- [Fertility](./fertility.md) - Island resource availability and regional differences
+
+## City Management
+- [Citizen Needs](./citizen-needs.md) - Goods and services required by each population tier
+- [City Status](./city-status.md) - Population thresholds, bonuses, and penalties
+- [Health, Happiness & Fire Safety](./health-happiness-fire.md) - Incident prevention and City Watch
+
 ## Infrastructure
 - [Shipyard](./shipyard.md) - Ship construction system
 - [Warehouse Cloud](./warehouse-cloud.md) - Shared island storage