Which of these would undermine the key principles of mercantilism?

A. free trade

B. taxation

C. tolls

D. ending piracy

Correct answer is A. free trade.

Mercantilism was an economic system averse to competition. It relied on mechanisms such as heavy taxation of imports, monopolies, exclusive trade agreements, colonialism and eventually even trade wars to secure the interests of the merchants. Therefore, a nation that promoted free trade would not be in accordance to the principles outlined by mercantilist therorists, who saw the world's amount of wealth as static and recommended that governments resort to tariffs on foreign imports and the maximization of exports.