When general war broke out in August 1914, few people shared Albert Einstein's gloomy assessment that 'Europe, in her insanity, has started something almost unbelievable'. In towns and cities across the continent, the various declarations of war in late July and early August were greeted with displays of patriotic euphoria. Generals and politicians commonly believed that this would be a short conflict, bringing in its wake opportunities to settle old scores and to acquire new territories.

The mood of bellicose optimism did not last long. The First World War was to last for more than four years. It cost more than nine million lives and left behind a devastating legacy of political change, economic hardship and social dislocation.

Few topics in 20th-century history have caused as much controversy as the debate surrounding the origins of the First World War. The eventual Allied victory in 1918, and the subsequent move to blame Germany for the outbreak of the conflict through the 'war guilt clause', laid the foundations for a bitter and enduring debate that still fascinates historians today.

The immediate trigger for war in the summer of 1914 was the assassination of the heir to the Habsburg throne, Archduke Franz Ferdinand, by the Bosnian-Serb nationalist Gavrilo Princip in Sarajevo on 28 June. This event led directly to Austria-Hungary's declaration of war on Serbia a month later and the subsequent entanglement of Europe's other Great Powers in a general war by 4 August.

However, the root causes of this conflict were to be found in the many and varied Great Power rivalries of the late 19th and early 20th century. They found expression both inside Europe - where a delicate series of alliances maintained the 'balance of power' - and elsewhere in the world, as the era of empire-building reached its peak.

Germany, a latecomer to Great Power status, feared encirclement by France and Russia and resented Britain's naval supremacy. French enmity towards Germany was forged by the humiliating territorial losses of Alsace and Lorraine during the Franco-Prussian war of 1870-71.

Russia and Austria-Hungary, both multinational empires with severe domestic problems, were at loggerheads in the Balkans, where Russia's pro-Slav tendencies clashed with Austria-Hungary's desire to curb demands for Slav autonomy within its borders. Finally, there was Britain, whose pre-eminent position as a colonial, naval and commercial power in 1914 encouraged intermittently tense relations with France, Russia and Germany.

The following references give an idea of the sources held by The National Archives on the subject of this chapter. These documents can be seen on site at The National Archives.