Mercantilism was an economic theory that posited that the richer a nation was,the more powerful it would be.It was the dominant economic system in the West throughout the 18th century.
Colonies could be exploited for cheap raw materials - furs,lumber,fish and so on - that could be used to feed the home populations of the colonizing countries,and for use in producing manufactured goods in these countries.America had all these things in abundance,which encouraged European colonization there.