British mercantilist writers were themselves divided on whether domestic controls were necessary. British mercantilism thus mainly took the form of efforts to control trade. A wide array of regulations were put in place to encourage exports and discourage imports. Tariffs were placed on imports and bounties given for exports, and the export of some raw materials was banned completely. The Navigation Acts removed foreign merchants from being involved England's domestic trade. British policies in their American colonies led to friction with the inhabitants of the Thirteen Colonies, and mercantilist policies (such as forbidding trade with other European powers and enforcing bans on smuggling) were a major irritant leading to the American Revolution.