Mercantilism was a reaction against the economic problems of earlier times when states were too weak to guide their economies and when every town or principality levied its own tariffs on goods passing through its borders.
Mercantilism was the theory of trade espoused by the major European powers from roughly 1500 to 1800. It advocated that a nation should export more than it imported and accumulate bullion (especially gold) to make up the difference. The exportation of finished goods was favored over extractive industries like farming
Mercantilism is the economic doctrine in which government control of foreign trade is of paramount importance for ensuring the prosperity and security of the state. In particular, it demands a positive balance of trade. Mercantilism dominated Western European economic policy and discourse from the 16th to late 18th centuries. Mercantilism was a cause of frequent European wars in that time and motivated colonial expansion.
Mercantilism was the dominant school of thought in Europe throughout the late Renaissance and early modern period (from the 15th-18th century). Mercantilism encouraged the many intra European wars of the period and arguably fueled European expansion and imperialism both in Europe and throughout the rest of the world until the 19th century or early 20th century.
The modern age brought the rise of powerful nation states (Holland, France, Spain and England) and was marked by almost constant warfare. Money (bullion) was needed to support ever-expanding armies and navies. Mercantilist concepts developed from this need. Underlying this theory was the belief that wealth was finite. If one nation hoped to grow richer, it had to do so at the expense of some other nation. The development of colonies became very attractive during this era. Wealth could be kept by a nation if its colonies provided raw materials to the mother country and the mother country could sell finished goods to the colonies.
Reverse-mercantilism is an economic system which strives to increase corporate wealth and monopoly by subsidizing some corporate entities while regulating, taxing and controlling borders (blocking outsourcing and creating tariffs) for all competitors.
We can conclude that mercantilism was a reaction against the economic problems during 18th century and also was a doctrine in which government control de security and prosperity of the state and also the importing and exporting of the country.