Trade barriers in the colonies were designed to ensure that the colonies primarily traded with Britain, aligning with Britain's mercantilist economy. This economic theory emphasized that a nation's strength depended on its wealth, which could be increased through a favorable balance of trade.
Thus, the correct response is: Trade barriers made it difficult for the colonists to trade with any but British companies.
This restriction ensured that all trade flowed through Britain, allowing Britain to control colonial commerce and benefit economically from the colonies' resources and markets, reinforcing the mercantilist system.