Great question, the contributions of Britain’s colonies are well worth examining. I’m in the middle of looking at French colonial forces at the moment and intend to write about Britain’s imperial forces in more depth in the future.
Canadian Army: 1914
29th Battalion, (Vancouver), Canadian Expeditionary Force, mustered at Hastings Park, Vancouver - Winter 1914, (source)
The Canadian Army proper came into existence on the Confederation of Canada in 1867. Prior to this the British army had stationed regular army battalions in Canada to garrison strategic positions and of course there was also the Canadian militia. By the 1880s the Permanent Active Militia had been formed, a professional forces made up of volunteers - in effect Canada’s regular army. This was accompanied by the larger Non-Permanent Active Militia which was a semi-professional volunteer force made up of a dozen or so reserve units - many of whom would volunteer when the war began.
The size of the Permanent Active Militia in 1914 was approximately 5,000 men forming one regiment of infantry and two of cavalry. While the larger part-time Non-Permanent Active Militia numbered perhaps a dozen regiments and artillery detachments. During the Boer War over 7,000 Canadians volunteered for service. Following involvement in the Boer War the Canadian government had formed many of the support corps necessary for fighting a modern war, these included the Signalling Corps, Army Service Corps and the Ordnance Stores Corps.
When Britain declared war on Germany on the 4th August 1914, Canada as a senior dominion of the British Army automatically declared war on Germany as well.
However, in 1914 the Permanent Active Militia did not make up the force which was sent to France by the Canadian government. Again, as during the Boer War this force was formed from Volunteers although on a much more organised scale. The Canadian Expeditionary Force began to form in the late summer of 1914 and by late 1914 the first units had set sail for Britain, they initially formed a single division numbering approximately 20,000 men - they first saw action in early 1915, at the Second Battle of Ypres. The Canadian Ministry of Militia and Defence were responsible for the formation, supply and training of the new army. The men who volunteered initially came from many of Canada’s militia units as well as from the general public. It was not until 1917 that conscription was introduced.
Canada’s expeditionary forces continued to grow and by September 1915, there were enough men in Europe to form a solely Canadian Corps which could fight independently. The Corps grew from 35,000 to almost 100,000 men by 1917. By the end of the war some 640,000 men had enlisted with 60,600 men losing their lives.
‘The Canadian Expeditionary Force’, CWM (source)
'Soldiers of the First World War: 1914-1918’, Library and Archives Canada (source)