In the summer of 1914, Britain was the world's strongest naval, colonial and financial power. When the First World War ended more than four years later, its place in the world no longer seemed so secure. Historians now generally acknowledge that the war contributed significantly to Britain's gradually declining status as a global power in the 20th century. How and to what extent did it also change British politics and society?

In 1914, the British army was relatively small, consisting of just over 730,000 officers and men. One-third of them served in the regular army itself, with the greater part stationed in reserve formations, the most notable of which was the Territorial Force. The majority of officers were recruited from Britain's long-established public school élite. Many of the army's rank and file were unskilled (and often unemployed) labourers.

The outbreak of war rapidly changed this situation. Increased recruitment to the British army suddenly became imperative. Lord Kitchener, the newly appointed war secretary, decided not to rely solely on the Territorial Force as the basis for expansion. Until the end of 1915, volunteers for military service were instead organised into units of what became known as the New Army.

Of the three main components of the British army during the First World War - the regulars, the Territorials and Kitchener's volunteers - it was the last group that attracted the most attention. The New Army provided 30 additional infantry divisions in 1914 and 1915, many of which contained 'Pals' battalions made up of groups with shared local, professional or social backgrounds. Kitchener's volunteers were at the centre of the brief 'rush to the colours' of August and September 1914, a mood captured in the famous recruitment poster featuring a drawing of Kitchener next to the caption 'Your country needs you'.

Men from the British empire and Dominions also rushed to enlist at the beginning of the war. The Australia Imperial Force, for example, was formed in September 1914. The Indian army was also quick to contribute. However, the British government delayed the formation of the British West Indies Regiment until 1915, and thereafter used the troops mainly as labourers.

Of all the major powers involved in the conflict, Britain was the only one still reliant on a volunteer army. However, given the high casualty rates on the Western Front, a policy of voluntary enlistment could not be sustained indefinitely. From the spring of 1915 onwards, the minister of munitions David Lloyd George, backed by the Conservative party and the newspapers of Viscount Northcliffe, pushed for the introduction of conscription. Asquith attempted to delay or at least limit it - based on the long-standing Liberal opposition to a 'standing army' - throughout 1915. But he was fighting a losing battle.

In January and May 1916, two Military Service Acts were passed, ensuring that all British men were now eligible for conscription. Although it was only in 1917 that Britain finally had more troops on the Western Front than it did at home, conscription marked a new level of commitment to the war against the Central Powers. Its introduction did not, however, go unchallenged.