Relationship between imports and exports in a mercantilist economic system?

The relationship between imports and exports in a mercantilist economic system is that one superpower dominates the imports and exports of another country. To further explain this, here is an example: when the British still held control over the American colonies they only let the colonies import from Great Britain and export to Great Britain, so that Britain was the only country to gain from this while the other European superpowers and the colonies were halted from making economic gains.