S.R. Ashton 
British Policy Towards the Indian States 1905-1939 [PDF ebook] 

British Policy Towards the Indian States (1982) examines the concept of indirect rule in terms of both its application and consequences in the princely states of India during the first four decades of the twentieth century. The author first deals with the political geography and diversity of the princely states and the legacy of the Mughal emperors, and then proceeds to discuss the nature and consequences of the alliances established between the paramount power of the British Raj and the princes at the beginning of the twentieth century. The impact of the non-interference policy is assessed and a full consideration is given to the failure of that policy.