What is the main idea of mercantilism?

Mercantilism is customary to call the system of ideas and views in the 15-17 centuries, the authors and supporters of which believed that the economy needed protection from the state. The state needed to impose high taxes and duties on imports, as well as support and subsidize the national producer of goods. The author of this doctrine was the Frenchman Montchretien. Mercantilism itself was initially popular in the English kingdom when it fought trade wars with the Netherlands in the 16th and 17th centuries. The main supporter of this policy in the economic sphere on the territory of the Russian Empire was Nicholas I.