It was the War To End All Wars, but the aftershocks are still being felt today. On the 90th anniversary of Britain's declaration of war against Germany, Nick Morrison looks at the origins of the First World War - and its legacy

JUBILANT crowds surged through the streets of London and other major cities; thousands of people gathered outside Buckingham Palace to sing the National Anthem; the Prime Minister was cheered as he rose in the House of Commons; young men flocked to the recruiting offices. It was August 4, 1914, and Britain had declared war on Germany.

Amid the national euphoria was a widespread belief that it would all be over by Christmas: British resolve and French offensive lan would soon put the Germans on the back foot and bring a swift end to the war.

Lord Kitchener was one of the few dissenting voices. He announced his intention to recruit 100,000 volunteers for a new army. It was to take many more than that before the war was out.

The Great War was to leave an estimated ten million people dead and millions more injured in both body and mind. But the repercussions went further even than that. Imperial dynasties were swept away and new republics created; communism took hold in Russia and laid the foundations for a 40-year Cold War; the United States ended its isolationist approach to the world; perhaps most chillingly, the stage was set for the rise of Hitler, the Holocaust, the Second World War and the nuclear age.

But the causes of the war are, even 90 years on, far from clear.

Tensions between the European powers had been rising for some time, heightened by instability in the Balkans and German aggression under Kaiser Wilhelm II.

A complicated network of alliances had been put in place to try and keep the peace, attempting to ensure that too much was at stake for any one state to act unilaterally, but the downside was that if one brick was removed, the whole edifice would fall. And all the time the developing arms race merely confirmed that war was inevitable.

The trigger was the assassination of Archduke Franz Ferdinand in Sarajevo on June 28. The heir to the Habsburg empire had been shot by Gavrilo Princip, a 19-year-old student, who told police he wanted to take revenge for the oppression of the Serbian people.

Austria suspected Serbian involvement in the assassination and made a series of humiliating demands on the Serbian government, which were rejected. Supported by Germany, Austria then began an invasion.

Russia began to mobilise in support of its ally, Serbia, and in response the Kaiser declared war on the Czar. France came to the aid of its ally, Russia, and Germany and France declared war on each other. Germany demanded passage through Belgium, whose neutrality had been guaranteed by Germany, Britain and France since 1839.

Britain told the Kaiser that it would stand by its treaty obligation, so when the Germans invaded Belgium, Prime Minister Herbert Asquith declared that Britain was at war.

More than one million men signed up within the first three months of the war, in what was the first large-scale voluntary enlistment in British history. For the first time, ordinary citizens were told that they should lay down their lives for the good of the nation.

The war marked a stark departure from previous military engagements. Britain's recent military history was of a series of colonial wars, pitched battles where one side could claim to be the victor and which had little direct impact on the population at home other than as causes for rejoicing or otherwise.

Now, the full resources of the nation were directed towards the war effort in what became a war of attrition, with each side making gains, only to lose them again. For the most part, this constant advance and retreat replaced the single, decisive battle, as trench warfare made conventional battle plans redundant.

Life in the trenches was cramped, miserable and harsh. Trench foot became endemic, a result of standing in waterlogged trenches for hours on end, and could lead to gangrene and amputation. During the first winter of the war, more than 20,000 men in the British Army were treated for trench foot.

Dysentery and lice were common, but the psychological effects of battle were perhaps even more serious. More than 80,000 British soldiers suffered from shell shock, and many more suffered mental breakdowns. Some shot themselves in the foot or hand to try and get sent home from the front; some deserted and were captured and shot; some killed themselves rather than face the continuing horror.

Life expectancy was short, as both sides became bogged down and, after the rapid gains and losses of the first few months, unable to move more than a few miles. In the British Army, junior officers had the highest casualty rate, higher even than the ordinary soldiers, wiping out what came to be known as the lost generation.

To try and break the deadlock, the generals and politicians resorted to ever-more desperate tactics. Believing that one great push was all it needed, the commander of the British forces, General Douglas Haig, sent 750,000 men over the top in July 1916.

The first day of this Battle of the Somme was the bloodiest day in the British Army's history, as almost 20,000 soldiers were killed and 40,000 injured. By the time the battle was over, the Allies had suffered more than 600,000 casualties and had advanced just a few miles.

But just as it ushered in one new type of war, it also saw the first signs of trench warfare's replacement, the advent of technology-based warfare. Tanks and planes made their first appearances in warfare, although too late and in too small a number to make a significant difference.

The United States entered the war in April 1917, ending more than 100 years of a determination to stay above alliances, with public opinion galvanised by the sinking of US ships by German submarines.

In spring 1918, the Germans launched a major offensive but when early gains failed to stick and advance turned into retreat, it became clear there would be no victory. In the face of mounting unrest at home and demoralised workers threatening revolution, the new German government surrendered unconditionally.

By the time an armistice was declared, on November 11, 1918, more than 42 million men had been mobilised in the Allied war effort. Of those, more than five million had died, including three million French and Russians. Germany and its allies had mobilised 23 million men, and lost almost 3.5 million. A total of ten million people are thought to have died, with another 21 million soldiers wounded.

The number of British deaths as a result of the war is put at 744,702.

The war also carried a huge financial cost, draining reserves and leaving the British economy weak, in turn leading to industrial unrest, economic instability and the replacement of the Liberals by Labour as the main opposition to the Conservatives.

In Russia, the revolution in 1917, driven by revulsion at the war and food shortages which left millions on the verge of starvation, saw the autocratic Czarist regime replaced by the Bolsheviks, who were to surpass their predecessors in brutality, ushering in more than 70 years of communist oppression.

The Kaiser's abdication in the face of growing disillusionment with his rule saw Germany become a republic, but the terms of the Treaty of Versailles left the Germans both aggrieved and economically crippled, as well as ready for a ruler who would promise to restore national pride. Adolf Hitler capitalised on this resentment, first to propel him to power and then to fuel his expansionism, which was to result in the Second World War.

In turn, this was to lead to the creation of the European Union, as the continent sought to heal its wounds, and the creation of Israel, as the scale of the Holocaust and the persecution of Jews became clear.

And there are a myriad further consequences of the war: from the creation of Balkan states out of the ashes of the Austro-Hungarian Empire, to the creation of a bureaucracy in Britain to run the war effort which has never been rolled back; from the League of Nations, forerunner of the United Nations, to votes for women, in recognition of their contribution in munitions factories.

But perhaps the most durable effect of the war was psychological. The aftermath of the war saw widespread criticism of the tactics which had led so many men so apparently needlessly to their deaths. As the "lions led by donkeys" belief took hold, so the deference towards the ruling class began to be shaken.

Soldiers may have obeyed their officers unquestioningly in going over the top, but belief in authority suffered a mortal blow. As the proclamation that it was the War To End All Wars turned out to be wrong, so the demands of the state lost their inviolability. The war may be long over, but the wounds are still there.