Although she kept in contact with Polish socialists, she moved to Germany in May 1898 to work in the Social Democratic Party (SPD) and established her reputation as a brilliant political writer with the booklet Social Reform or Revolution (1899). During Russia's 1905 revolution she went to Warsaw and was imprisoned for a short time. She returned to Berlin and became a teacher in the SPD school (1907–14), where she set out her interpretation of Marxism in The Accumulation of Capital (1913), published in English in 1951.
During World War I Luxemburg joined Karl Liebknecht in organizing the Spartacus League, out of which grew the German Communist Party. She was in prison during most of the war, but her writings, such as The Crisis in the German Social Democracy and the Spartacus Letters, continued to appear. Released in 1918, she reluctantly supported an unsuccessful uprising, known as the Spartacist Revolt, against the government. Although she was very critical of the Russian Bolsheviks' dictatorship, her ultimate aim in Berlin was a new government based on workers' councils something like those introduced during the Russian Revolution.
Luxemburg's studies of capitalism modified Marx's ideas by considering the new role of imperialism. In The Accumulation of Capital she argued that capitalism would survive until it dominated the whole world through imperialist expansion. Her theory stressed the potential revolutionary energy of the common people. Rejecting Lenin's Russian party structure, she favoured instead an organization with internal democracy and mass participation. Luxemburg's considerable influence was due as much to her life of courageous action as to her theory. Although crippled from childhood and plagued with poor health, she never shunned work or danger. Her murder in Berlin by soldiers who were later acquitted of the crime made her a martyr and enhanced her reputation among radicals.