trans-atlantic trade promoted colonies since colonial powers could now use foreign nations as a trading post and get cheaper, government-subsidized products by colonizing places with different exports. Mercantilism promotes imperialism, tariffs and subsidies on traded goods to achieve peak economical strength, so it's no surprise imperialist powers used tariffs on colonists and subsidies on colonial goods in their home countries! Also, mercantilism promotes exports and minimizes imports (sound familiar? colonies were sort of puppet organizations of a larger empire, where the colonies would just export goods the empire wanted to trade with or buy cheaper).
