Many philosophical ideas have given rise to or been associated with various ideologies. A radical example is dialectic-materialism based on the philosophical work of Marx and Engels, which became the official credo of communist countries in the 20th century. Another instance is Nietzsche's philosophy, distorted to such an extent that it was linked to movements such as Nazism. These may be extremes, but other philosophies have also been used to justify ideological ends - for instance, an impoverished interpretation of Adam Smith's work (via economist Milton Friedman) was popular during Thatcherism. As in the other cases, such ideologies are usually distortions and simplifications of the original thought that contradict the impartiality of philosophical argument and severely restrict its independence. Philosophy properly conceived should not be one more form of power, but a counter to external power.