The Commercial Revolution was a period of economic expansion, colonialism, and mercantilism that lasted from approximately the 16th century until the early 18th century. Beginning with the Crusades, Europeans rediscovered spices, silks, and other commodities rare in Europe. This development created a new desire for trade, which expanded in the second half of the Middle Ages. European nations, through voyages of discovery, were looking for new trade routes in the fifteenth and sixteenth centuries, which allowed the European powers to build vast, new international trade networks. Nations also sought new sources of wealth. To deal with this new-found wealth, new economic theories and practices were created. Because of competing national interest, nations had the desire for increased world power through their colonial empires. The Commercial Revolution is marked by an increase in general commerce, and in the growth of non-manufacturing pursuits, such as banking, insurance, and investing.