
During World War 1, the French and British were able to draw on extensive manpower resources from their vast colonial empire. The British relied heavily on soldiers from their Indian colonial possessions, particularly the Sikhs, who fought for the British in all of the theatres of war, and mainly in the Middle East and on the Eastern front.
The French drew colonial troop levies from its African possessions. Algerian and Senegalese troops fought alongside their colonial overlords in a war which they had no part of and to maintain an imperial system that many despised. Nevertheless it is true that the contribution made by the French colonial soldiers was appreciated by the French.
The poster at the top advertises the Day of the Army of Africa and the Colonial Troops. It depicts a number of soldiers from various parts of the empire, likely from North Africa, fighting under the banner of France.
Below is a photograph of French citizens showing their gratitude to the French colonial troops by offering wine to some Algerian soldiers as their train stops at a railway station on the way to the front.

The Algerians must not have been offended by the offer of wine, nominally against their religion, as they are obviously glad for the offer. Such scenes of goodwill were genuine. The French realized the great debt that they owed their colonial empire and in addition to spontaneous gestures like these, the government also made sure to acknowledge the contribution made. The posters were not so much for the benefit of the colonial troops as for the morale of the French civilians; they were meant to convey the fact that the French were not alone and they had great and vast reserves of soldiers with which to win the war.
The poster below is devoted to extolling the contribution of the African troops, which are portrayed somewhat stereotypically and in a way that would be considered offensive today. However the mere fact that Africans were being portrayed as brave warriors fighting for the motherland of France was a step forward in race relations and understanding.

The hardships faced by the colonial troops were particularly severe, even compared to the generally hellish conditions of world war 1. Far from home, in an alien environment, fighting for an empire which gave them few rights or benefits, they were forced to fight with second rate equipment in a cold climate that was foreign to them. They were often used as expendable troops even in the context of the general callousness with which the allied generals sacrificed their men.