Orthodox Marxism
Orthodox Marxism is contrasted with revisionist Marxism as developed in post-First World War Social Democratic parties. Some writers also contrast it with Marxism–Leninism as it developed in the Soviet Union, while others describe the latter as firmly within orthodoxy: Orthodox Marxism rested on and grew out of the European working class movement that emerged in the final quarter of the 19th century and continued in that form until the middle years of the twentieth century. Its two institutional expressions were the 2nd and 3rd Internationals, which despite the great schism in 1919, were marked by a shared conception of capital and labour. Their fortunes therefore rose and fell together. Trotskyism and Left communism were equally orthodox in their thinking and approach, and therefore must be considered left-variants of this tradition.