Yesterday marked the 100th anniversary of Britain’s declaration of war against Germany, which completed the entry of all the European imperialist powers into World War I.

The British declaration of war was issued on the pretext that the neutrality of Belgium, which it was committed to protect, had been violated by Germany’s declaration of war against France on August 3 and its deployment of troops on Belgian soil.

Germany’s war declaration had been carefully orchestrated to ensure that it took place after the troop mobilisation by France’s ally, Russia. The Russian mobilisation, in turn, had been prompted by Austria’s declaration of war on Serbia on July 28, which Russia pledged to defend in accordance with its expansionist aims in south-eastern Europe.

Over the next four years, the propaganda machines of the imperialist powers were to be honed and developed in order to cover up their real war aims.

Britain, it was claimed, had intervened to counter the atrocities of the “Hun” and defend the “rights of small nations”—notwithstanding the fact that “little Belgium” was an imperialist power in its own right, with considerable colonial holdings in Africa.

France, its political leaders insisted, was fighting the war to uphold the ideals of liberty and democracy against Prussian militarism, despite the fact that it was in alliance with the autocratic and blood-soaked tsarist regime in Russia, supplying it with huge loans that helped sustain the military and the repressive apparatus of the state.

Germany maintained it had been forced into war by the actions of the other European powers and was fighting against Russian barbarism in defence of European culture, as it sought to dominate Europe and achieve its “place in the sun” as a global power.

In fact, the war was not waged for “democracy,” the rights of small nations, or to defeat authoritarianism, but for markets, profits, colonies and spheres of influence. In a rare moment of candour, Winston Churchill, at that time first lord of the admiralty, explained that Britain had an empire, acquired by violence and maintained by force, which others sought to obtain.

While the political superstructure of Europe was very different than what exists today—there was a German kaiser, a Russian tsar and an Austrian emperor—the driving forces of the war were rooted in the capitalist economy.

As Leon Trotsky explained, in words that resonate so powerfully in today’s era of globalised production, the vast economic expansion that had taken place over the preceding 40 years meant that the world—the land, the sea, the interior (and today we could add outer space)—had become a single economic workshop. World economy as a whole had replaced the nation-state as the centre of economic development. But the world remained divided by the nation-state system, dominated by the imperialist powers.

In short, the development of mankind’s productive forces—the basis for the economic advancement of the world’s people—had come into conflict with the nation-state framework in which the capitalist profit system is rooted.

Imperialism, Trotsky wrote, proposed to resolve this contradiction through a bloody struggle of each against all to determine which of the capitalist great powers would become a hegemonic power. War was the method by which capitalism, at the climax of its development, sought to resolve this insoluble contradiction.

The only progressive solution was not the victory of one or another imperialist power, but the overthrow of the capitalist system—the source of the eruption of imperialist violence and destruction. The program of world socialist revolution had become the order of the day.

But if the war laid bare an historic crisis of the capitalist system, it no less powerfully revealed a deep crisis in the workers’ movement. On August 4, 1914, as the guns started to fire, the French and Germany socialist parties—the French Section of the Workers International (SFIO) and the German Social Democratic Party (SPD)—voted to support their own governments.

The Second International, of which they were the two major sections, had pointed to the danger of war over the preceding period. At its congress in Basel in 1912, it had voted to commit its sections to a struggle against war, and, if it proved impossible to prevent, to utilise the crisis created by war to hasten the overthrow of capitalism. That commitment had been torn to shreds. The Second International was dead for the purposes of socialism.

The most far-reaching conclusions were drawn by the then relatively little known Marxist leader Vladimir Lenin. The answer to the question as to why the Second International had betrayed, he explained, was not to be found simply in the political biographies of the individual leaders, important as it was to examine them. It signified, above all, the end of a whole epoch—the peaceful, organic development of capitalism, in which the Second International had been founded and grown—and the dawning of a new one: an epoch of wars and revolutions.

The overriding question for Lenin was not the development of tactical slogans for the mass movement that he was sure would develop against the war, but the question of a perspective to guide it. It was necessary to grasp that the socialist revolution was not some distant event that would one day arrive, but rather a historical process that had to be actively prepared and consciously directed. That was the meaning of his call to “turn the imperialist war into a civil war.”

Furthermore, it was necessary, without waiting for a mass movement to emerge, to found the Third International as the international revolutionary leadership of the working class. That was the essential pre-condition for the taking of political power by the working class when the masses were driven into struggle against the capitalist barbarism of the war.

The building of the Third International, Lenin insisted, took place through the most relentless struggle against all forms of opportunism—not only against the right wing in the Second International that had overtly carried out the betrayal, but against those “lefts” who covered up for them.

It was on this perspective that, under the leadership of Lenin and Trotsky, the Bolshevik Party carried through the Russian Revolution in October 1917 as the first shot in the world socialist revolution.

Lenin played a unique role, because his whole struggle to build the Bolshevik Party had been based on an unrelenting struggle against opportunism. What had appeared to his opponents as “sectarianism,” “doctrinarism,” and “tendentious hair-splitting” had a world-historic significance. It was the essential precondition for building a revolutionary party capable of meeting the tasks of the new epoch.

On the centenary of the outbreak of World War I, these lessons acquire a burning actuality, as the imperialist powers threaten to plunge humanity into a third world war. Not only are wars spreading in Syria, Iraq, Libya, Ukraine and beyond, which threaten to produce a clash with nuclear-armed powers such as Russia and China, but these wars have been embraced by the pseudo-left parties in the imperialist countries. As these wars spread, moreover, tensions grow between the imperialist powers themselves.

The role of building the necessary revolutionary leadership of the international working class in the struggle against capitalism falls to the Fourth International under the leadership of the International Committee, for which its protracted struggle against all forms of national opportunism, stretching back more than six decades, has been the decisive preparation.