"Britain went to war with Germany in August 1914 for similar reasons to those for which the country fought Hitler's Germany in the second world war: to prevent an authoritarian, militarist, expansionist enemy achieving hegemony in Europe and thus imperilling British security."

"Rather, the first world war was an existential struggle, just as much a war of national survival for the British as the second world war. If Britain and its allies had lost, it would have meant the end of liberal democracy on mainland Europe. As it was, civilians were kept docile in German-occupied France and Belgium by the routine use of terror. Forced labourers were deported to Germany under terrible conditions. Unlike Hitler's regime, the Kaiser's was not consciously genocidal, but it was aggressive and brutal enough. In 1918 the British army was fighting a war of liberation.

If Germany had won the first world war Britain, although probably safe from invasion thanks to the Royal Navy, would have been reduced to a state of siege, shut out of Europe. As British planners recognised during the first world war, had London been forced to come to terms with a victorious Germany, any peace could only have been temporary. Sooner or later Germany would have renewed the war and Britain and its empire would have been at a terrible disadvantage.

There is plenty of evidence that most ordinary British people understood what was at stake and, just as in 1939-45, more or less willingly committed to the struggle. The idea of mass war enthusiasm in August 1914 has been shown to be something of a myth. Instead, as the gravity of the situation became clear, there was a more nuanced response. One of the reasons why the support of the working classes for the war was so strong, even among those that lived in poverty, was the knowledge that they were better off than their parents and grandparents had been, and so had something to lose. "

"Today, horrified by the casualties of 1914-18, (which were consistent with losses of other belligerents), we tend to see the conflict in terms of what the war poet Wilfred Owen called the "pity of war". This is right and proper, but we should not lose sight of why the war was fought and the significance of the fact that it was Britain and its allies, and not Germany, that emerged victorious. Like all wars, it was tragic, but it was certainly not futile."

http://www.theguardian.com/commentisfree/2013/jun/17/1914-18-not-futile-war