Explain how mercantilism can negatively impact an economy?

mer·can·til·ism
noun
belief in the benefits of profitable trading; commercialism.
historical
the economic theory that trade generates wealth and is stimulated by the accumulation of profitable balances, which a government should encourage by means of protectionism.
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The basic definition is correct. The negative impact is from protectionism. When the government protects any business, it eventually regulates it to death. Railroads, for example.