In 1881, under the Cardwell-Childers reforms of the British Armed Forces, one pre-existent militia and seven volunteer battalions of Edinburgh, Midlothian, Berwickshire, Haddingtonshire and Linlithgowshire were integrated into the structure of the Royal Scots.
Many battalions of the Royal Scots were formed as part of Secretary of State for War Lord Kitchener's appeal for an initial 100,000 men volunteers in 1914.
The King's Regiment did not, however, return to its original peacetime size; it lost many of its territorial battalions shortly after the war ended.
As World War II approached, the Territorial Army was reorganised in the mid-1930s, many of its infantry battalions were converted to other roles, especially anti-aircraft.
In the immediate post-war period, the army was significantly reduced: nearly all infantry regiments had their first and second battalions amalgamated and the Supplementary Reserve disbanded.