In the second half of the 19th century, Islam was the only idea that made it possible for Indians to ally with their neighbours in an anti-imperial revolt. And though Communism, along with other challenges, soon came to join it, Islam remained an important threat until the mid-20th century. This was why Britain’s enemies, from Napoleonic France to Ottoman Turkey, as well as Germany in both world wars, encouraged a rebellion that might unite India’s Muslims with those outside in a movement that would overthrow their rival’s empire. Pan-Islamism created a model for international resistance in South and Central Asia, one that occupied a Bolshevik like Lenin as much as an imperialist like Curzon, each trying to appropriate as much as eliminate it. If the British Empire was routinely described by its upholders as “the world’s greatest Mohammedan Power”, it was in order to oppose Ottoman claims to Islamic leadership as much as to secure the loyalty of Muslims, who formed a large part of the Indian army that was used to exercise British control over Asia, Africa and West Asia, besides being deployed in Europe itself during both world wars.