Mercantilism, also called "commercialism," is the idea that the best way to improve a nation or state is by profiting off of goods and trade. During the colonial period (15th-19th century in North America) the most desired goods in Europe were exotics- silk from China, tea from India, chocolate from South America, sugar from the Caribbean, spices from Thailand, and so on. Expansion into North America and claiming new land for one's own country held the promise of profit, even if it meant stealing or engaging in genocide. One could rest assured that whatever resources they found on the land claimed for their mother country would be profitable simply because they were exotic to the Europeans.
Explorers and merchants traveling to and from the New World not only hoped to bring exotics into their country, they hoped that the sale of these goods would bring more gold and silver in the form of coinage. Colonies which specialized in exporting particular goods- such as sugar, tobacco, or furs- could expect to not only sell these in their home country but to merchants from much farther away. These merchants from nations which did not have a colony producing that particular good might be willing to pay even more and then profit off of the sale in their home country.
In an attempt to sustain the high demands of mercantile economic philosophy, a number of colonizing nations imported slaves and employed religious and cultural conversion as a means of ensuring free or cheap labor.