Final answer:
Indian soldiers played a crucial role in World War I, with over 700,000 fighting for Britain. Their significant contributions, however, did not immediately translate into the political gains they hoped for, leading to increased support for nationalism in India. True, Indian alliances and troops were critical to European imperial powers.
Step-by-step explanation:
The Indian participation in World War I was significant for several reasons. Over 700,000 Indian soldiers fought for the British Empire, and their contributions were crucial in several theatres of war, including Mesopotamia, Gallipoli, Egypt, German East Africa, and Europe. Many Indians held out hope that their service would result in greater autonomy or independence post-war. However, Britain did not initially plan for any change, leading to increased support for the nationalist movement in India post-WWI.
Colonial troops, including those from India, played a substantial role in the war efforts of imperial powers. The significant loss of life—at least 74,000 Indians died—did not promptly yield the political gains Indian soldiers and leaders had hoped for. Britain's reliance on Indian soldiers was even more pronounced in World War II, where 2.5 million Indian soldiers fought and over 87,000 were killed. The statement about Indian alliances being important for European empires in the southeast (presumably alluding to the Southeast Asian context) would be True with respect to the importance of colonial troops, including Indians during World War I.