On 4th August, 1914, Karl Liebknecht was the only member of the Reichstag who voted against Germany's participation in the First World War. He argued: "This war, which none of the peoples involved desired, was not started for the benefit of the German or of any other people. It is an Imperialist war, a war for capitalist domination of the world markets and for the political domination of the important countries in the interest of industrial and financial capitalism. Arising out of the armament race, it is a preventative war provoked by the German and Austrian war parties in the obscurity of semi-absolutism and of secret diplomacy."
Paul Frölich, a supporter of Liebknecht in the Social Democratic Party (SDP), argued: "On the day of the vote only one man was left: Karl Liebknecht. Perhaps that was a good thing. That only one man, one single person, let it be known on a rostrum being watched by the whole world that he was opposed to the general war madness and the omnipotence of the state - this was a luminous demonstration of what really mattered at the moment: the engagement of one's whole personality in the struggle. Liebknecht's name became a symbol, a battle-cry heard above the trenches, its echoes growing louder and louder above the world-wide clash of arms and arousing many thousands of fighters against the world slaughter."
Clara Zetkin later recalled: "The struggle was supposed to begin with a protest against the voting of war credits by the social-democratic Reichstag deputies, but it had to be conducted in such a way that it would be throttled by the cunning tricks of the military authorities and the censorship. Moreover, and above all, the significance of such a protest would doubtless be enhanced, if it was supported from the outset by a goodly number of well-known social-democratic militants.... Out of all those out-spoken critics of the social-democratic majority, only Karl Liebknecht joined with Rosa Luxemburg, Franz Mehring, and myself in defying the soul-destroying and demoralising idol into which party discipline had developed."
Immediately after the vote on war credits in the Reichstag, a group of SDP anti-militarist activists, including Ernest Meyer, Franz Mehring, Wilhelm Pieck, Julian Marchlewski, Hermann Duncker and Hugo Eberlein met at the home of Rosa Luxemburg to discuss future action. They agreed to campaign against the war but decided against forming a new party and agreed to continue working within the SPD.
In May 1915, Karl Liebknecht published a pamphlet, The Main Enemy Is At Home! He argued: "The main enemy of the German people is in Germany: German imperialism, the German war party, German secret diplomacy. This enemy at home must be fought by the German people in a political struggle, cooperating with the proletariat of other countries whose struggle is against their own imperialists. We think as one with the German people – we have nothing in common with the German Tirpitzes and Falkenhayns, with the German government of political oppression and social enslavement. Nothing for them, everything for the German people. Everything for the international proletariat, for the sake of the German proletariat and downtrodden humanity."
Over the next few months members of this group were arrested and spent several short spells in prison. On the release of Luxemburg in February 1916, it was decided to establish an underground political organization called Spartakusbund (Spartacus League). The Spartacus League publicized its views in its illegal newspaper, Spartacus Letters. Like the Bolsheviks in Russia, they began to argue that socialists should turn this nationalist conflict into a revolutionary war.
Dick Howard has argued: "Agitation continued throughout the war; yet the Spartacus League was never very strong. All agitation had to be carried out in strict secrecy, and the leaders were more often than not in jail." Members included Rosa Luxemburg, Karl Liebknecht, Leo Jogiches, Paul Levi, Ernest Meyer, Franz Mehring, Clara Zetkin, Wilhelm Pieck, Julian Marchlewski, Hermann Duncker and Hugo Eberlein.
Rosa Luxemburg argued that it was important to stop the First World War through mass action. This brought her into conflict with Lenin who had argued that "the slogan of peace is wrong - the slogan must be, turn the imperialist war into civil war." Lenin believed that a civil war in Russia would bring down the old order and enable the Bolsheviks to gain power. Luxemburg and Leo Jogiches took the side of the Mensheviks in their struggle with the Bolsheviks. As a result Lenin favoured the Polish section led by Karl Radek over those of Luxemburg.
On 1st May, 1916, the Spartacus League decided to come out into the open and organized a demonstration against the First World War in the Potsdamer Platz in Berlin. One of those who attended reported: "It was a great success. At eight o'clock in the morning a dense throng of workers - almost ten thousand - assembled in the square, which the police had already occupied well ahead of time. Karl Liebknecht, in uniform, and Rosa Luxemburg were in the midst of the demonstrators and greeted with cheers from all sides." Several of its leaders, including Karl Liebknecht and Rosa Luxemburg were arrested and imprisoned. They were not released until October, 1918, when Max von Baden granted an amnesty to all political prisoners.
In November 1918 Eugen Levine went on speaking tours in support of the Spartacus League. According to Rosa Levine: "His first propaganda tour through the Ruhr and Rhineland was crowned with almost legendary success... They did not come to get acquainted with Communist ideas. At best they were driven by curiosity, or a certain restlessness characteristic of the time of revolutionary upheavels... Levine was regularly received with catcalls and outbursts of abuse but he never failed to calm the storm. He told me jokingly that he often had to play the part of a lion-tamer."
Karl Radek, a member of the Bolshevik Central Committee, argued that the the Soviet government should help the spread of world revolution. At the end of the First World War Radek was sent to Germany and with a group of radicals who had been members of the Spartacus League, including Rosa Luxemburg, Karl Liebknecht, Max Levien, Eugen Levine, Leo Jogiches, Paul Levi, Wilhelm Pieck, Julian Marchlewski, Hermann Duncker, Hugo Eberlein, Paul Frölich, Wilhelm Pieck, Ernest Meyer, Franz Mehring, Rosa Levine and Clara Zetkin, helped to establish the German Communist Party (KPD) in December, 1918.
In Germany elections were held for a Constituent Assembly to write a new constitution for the new Germany. As a believer in democracy, Rosa Luxemburg assumed that her party would contest these universal, democratic elections. However, other members were being influenced by the fact that Lenin had dispersed by force of arms a democratically elected Constituent Assembly in Russia. Luxemburg rejected this approach and wrote in the party newspaper: "The Spartacus League will never take over governmental power in any other way than through the clear, unambiguous will of the great majority of the proletarian masses in all Germany, never except by virtue of their conscious assent to the views, aims, and fighting methods of the Spartacus League."
As Rosa Levine pointed out: "It had the advantage of bringing the Spartacists closer to the broader masses and acquainting them with Communist ideas. Nor could a set-back, followed by a period of illegality, even if only temporary, be altogether ruled out. A seat in the Parliament would then be the only means of conducting Communist propaganda openly.It could also be foreseen that the workers at large would not understand the idea of a boycott and would not be persuaded to stay aloof; they would only be forced to vote for other parties."
On 1st January, 1919, at a convention of the Spartacus League, Luxemburg was outvoted on this issue. As Bertram D. Wolfe has pointed out: "In vain did she (Luxemburg) try to convince them that to oppose both the Councils and the Constituent Assembly with their tiny forces was madness and a breaking of their democratic faith. They voted to try to take power in the streets, that is by armed uprising. Almost alone in her party, Rosa Luxemburg decided with a heavy heart to lend her energy and her name to their effort."
In January, 1919, Karl Liebknecht, Rosa Luxemburg, Leo Jogiches and Clara Zetkin organised the Spartakist Rising that took place in Berlin. Friedrich Ebert, the leader of the Social Democrat Party and Germany's new chancellor, called in the German Army and the Freikorps to bring an end to the rebellion. By 13th January the rebellion had been crushed and most of its leaders, including Liebknecht and Luxemburg. They were both murdered while in police custody.
Paul Frölich, the author of Rosa Luxemburg: Her Life and Work (1940) has explained how Luxemburg died: "A short while after Liebknecht had been taken away, Rosa Luxemburg was led out of the hotel by a First Lieutenant Vogel. Awaiting her before the door was Runge, who had received an order from First Lieutenants Vogel and Pflugk-Hartung to strike her to the ground. With two blows of his rifle-butt he smashed her skull. Her almost lifeless body was flung into a waiting car, and several officers jumped in. One of them struck Rosa on the head with a revolver-butt, and First Lieutenant Vogel finished her off with a shot in the head. The corpse was then driven to the Tiergarten and, on Vogel's orders, thrown from the Liechtenstein Bridge into the Landwehr Canal, where it was not washed up until 31 May 1919."