Orthodox Marxism is the body of Marxist thought which emerged after the death of Karl Marx and Friedrich Engels in the late 19th century, expressed in its primary form by Karl Kautsky. Kautsky's views of Marxism dominated the European Marxist movement for two decades, and orthodox Marxism was the official philosophy of the majority of the socialist movement as represented in the Second International until the First World War in 1914, which caused Kautsky's influence to wane and brought to prominence the alternative orthodoxy of Vladimir Lenin. Orthodox Marxism aimed to simplify, codify and systematize the Marxist method and theory by clarifying perceived ambiguities and contradictions in classical Marxism. Orthodox Marxism maintained that Marx's historical materialism was a science which revealed the laws of history and proved that the collapse of capitalism and its replacement by socialism was inevitable. The implications of this deterministic view were that history could not be "hurried" and that politically workers and workers' parties must wait for the material economic conditions to be met before the revolutionary transformation of society could take place. For example, this idea saw the Social Democratic Party of Germany (SPD) adopt a gradualist approach, taking advantage of bourgeois parliamentary democracy to improve the lives of workers until capitalism was brought down by its objective internal contradictions. The use of "orthodox" to refer to Kautsky's line is primarily to distinguish it from the reformism of Eduard Bernstein. Such "revisionists" were reviled by the orthodox Marxists for breaking with Marx's thought. The emergence of orthodox Marxism is associated with the latter works of Friedrich Engels, such as the Dialectics of Nature and Socialism: Utopian and Scientific, which were efforts to popularise the work of Karl Marx, render it systematic and apply it to the fundamental questions of philosophy. Daniel De Leon, an early American socialist leader, contributed much to the thought during the final years of the 19th century and the early 20th century.