Central to classical liberal ideology was their interpretation of John Locke's "Second Treatise of Government" and "A Letter Concerning Toleration", which had been written as a defence of the Glorious Revolution of 1688. Although these writings were considered too radical at the time for Britain's new rulers, they later came to be cited by Whigs, radicals and supporters of the American Revolution. However, much of later liberal thought was absent in Locke's writings or scarcely mentioned and his writings have been subject to various interpretations. For example, there is little mention of constitutionalism, the separation of powers and limited government.