Thirty-five nations joined in the War including such distant countries as Haiti, China, Brazil, and Siam (now Thailand). Still more nations under the empires fought. The British colonies of Nigeria, India, West Indies, South Africa, Rhodesia (Zimbabwe) and Kenya sent many men to fight on the Eastern Front. Troops from the French colonies of Morocco, Algeria and Senegal, and German colonies of Tanganyika (Tanzania) and Cameroon also joined. The empires wanted as many of their men as possible fighting in the war, hoping to achieve a quick win by overpowering their enemy with vast armies.

The British Expeditionary Force (B.E.F.) was relatively small in 1914 - only four divisions were sent in to France in August. Soldiers from almost every nation of the British empire increased its contribution, as well as its power and influence, during the conflict. Australia, Canada, New Zealand all offered assistance before the start of the war, however India was not given a choice. Some 161,000 trained soldiers in India could be ordered to mobilise while volunteers from Canada and Australia were trained and sent over.

The Dominion and Imperial forces showed their bravery in some of the toughest campaigns on the Western Front. Indian soldiers were in France by 1914, and suffered through the bitterly cold winter. Canadians took Vimy Ridge at the battle of Arras in 1917, where many French soldiers had perished in the disastrous Verdun battles. The ANZACs (Australian and New Zealand Army Corps) were killed in thousands at Gallipolli.