S1, E2: Historian David Olusoga explores how, when the European powers went to war, they immediately drew on the military resources of their respective empires. Sikhs, Gurkhas, Garhwalis and Pathans from the British Raj and Spahis, Zouaves and Senegalese from French North and West Africa were thrown into the front lines of World War I and were among the first to experience the hell of trench warfare.