Portugal trades to survive beside Spain

Portugal needed wealth because a much larger Spanish neighbor repeatedly threatened its independence and sometimes absorbed the kingdom before independence returned. Expansion across Iberia was constrained, so the viable direction was westward into the Atlantic and then through global sea routes. Commerce moved goods or services from places of abundance to places of scarcity. Necessities attracted heavy competition and low margins, while wants and luxury desires offered higher returns from wealthier customers. That logic explains why a small state would accept the risks of long-distance maritime trade.