Trade Route & Commerce Optimizer

Diplomatic favorability is the gatekeeper of profitable trade. At the highest favorability stage, tariffs drop to zero — your caravans move goods at pure price differential. At the lowest stage, trade routes cannot be established at all; the other side will refuse your merchants. The middle bands impose 10–35% tariffs that can erase the profit margin on low-value commodities like grain or firewood.

The optimizer above computes net profit as: (P_sell × (1 − Tax_dest) − P_buy) × Volume − (Distance × Cost_unit × (1 − RelayCount/10)). The relay-station term matters: every relay on the route reduces the per-tile transport cost by roughly 10%, up to a stacking cap. Long routes through relay chains can out-earn short direct routes.

A common strategic move is the 'tribute-then-trade' opening: pay a one-time knife-money tribute to jump favorability one band, then lock in a profitable long-term trade route at the new, lower tariff. The payback is typically 4–6 turns for a salt or bronze route.

Water routes carry 3× the cargo per trip but are constrained to river and coastline tiles. Land routes are flexible — you can build a trade post anywhere — but require a chain of relay stations to cover distance efficiently. On large maps, a hybrid network (water for bulk grain/fuel, land for high-value crafted goods) dominates either pure strategy.

Bandit risk scales with route length and is higher on land than water. The optimizer's risk coefficient factors into expected profit — a route that looks profitable on tariff math alone may be a net loss once you account for the probability of losing a caravan to raiders.