Final answer:
It was illegal for the French to trade with the Spanish primarily due to economic sanctions and political disputes, as Spain sought to maintain strict control over its colonies' trade and economic activities, which included limiting trade with nations like France.
Step-by-step explanation:
The French were prohibited from trading with the Spanish due to economic sanctions imposed by their respective governments, which were rooted in larger political disputes and efforts to control trade and commerce to benefit the home country. During the colonial period, Spain exercised stringent control over colonial trade.
Only a few ports were authorized for trading and licenses for trade were expensive, maintaining Spanish economic monopolies, including on mercury from Peru, which was crucial for processing precious metals.
At the same time, the Spanish Crown instituted reforms to maximize profits from its colonies, such as more effective tax collection and imposing monopolies that prohibited the colonies from freely trading with other nations, including France.
Meanwhile, actions like the Embargo Act of 1807, as proposed by President Thomas Jefferson, were intended to wield economic pressure as a weapon in foreign policy, affecting trade relations not only with Great Britain and France but also having indirect impacts on trade with other nations, like Spain.
Such economic policies stemmed from the broader diplomatic tensions and conflicts of the time, anchoring them within the realm of political strategy rather than religious or strictly economic reasons.