Greetings! Great question for sources, and imperial histories certainly have their bodies of literature to pick from. This response will soon be followed by another one from u/MaharajadhirajaSawai about sources for empires which existed on some part of the Indian subcontinent, and for a rather comprehensive list of sources on the Qing Empire, this recent writeup by u/EnclavedMicrostate should be of great use. For my part, I shall be providing some works (books and journal articles) for the British Empire. Let's begin.

Books

These three books are what I like to call the "Trilogy" on the British Empire, since in combination with each other they provide an excellent overview of the historical narrative and historiographical discussions on the Empire.

• The British Empire: A Very Short Introduction by Ashley Jackson (2013): Part of the rather good Oxford University Press series of Very Short Introductions, this work synthesizes all the major historiographical debates on the "true" nature of the British Empire from economic, cultural, political, and social points of view (each aspect has its own chapter in the work). By no means a comprehensive treatment of the empire, Jackson's work is one I would recommend as a first stop (if you will) for a general "demystification" reading on Britannia's imperial legacy and history.
• Unfinished Empire: The Global Expansion of Britain by John Darwin (2012): While I would recommend reading this larger book after Jackson's, it also serves as a rather good single-volume treatment of the British Empire from the larger aspects (economic, social etc.). Darwin goes more in-depth than Jackson, but also assumes that you have a general understanding of the Empire's growth and decline prior to reading the book (which is where Jackson's work comes in handy). Darwin is one of the current pre-eminent experts on the British Empire, and this work treats otherwise neglected areas of Britain's imperial past (i.e the role of religion and science) with great clarity and an engaging writing style.
• The Empire Project: The Rise and Fall of the British World-System, 1830-1970 by John Darwin (2009): Coming in at some 700 pages (not including 100 or so for footnotes and sources), this work is much larger than the other two combined, and for good reason. This book is much more technical in its discussion of the "World-System" which the British managed to build, hold, and finally lose in the 140 years discussed as part of the narrative. Engaging but thorough, Darwin's work also benefits from more words spent on analysing the specific parts of the Empire (an entire section is devoted to investigating the rise, nature, and oddities of each of the to-be dominions as well as India).

Articles

These articles range from secondary monographs on specific aspects of the Empire, to primary sources written while the Empire was very much a pre-eminent world power. All are available for free access on JSTOR using a personal account, and have been linked as well:

• On the British Dominions and their Legal Status:
  • Barker, Ernest. "GREAT BRITAIN AND THE BRITISH DOMINIONS." World Affairs 110, no. 2 (1947): 119-28. http://www.jstor.org/stable/20664434.
  • Dunn, Frederick Sherwood. "The New International Status of the British Dominions." Virginia Law Review 13, no. 5 (1927): 354-79. https://www.jstor.org/stable/1065201.
  • Elliott, W. Y. "The Sovereignty of the British Dominions: Law Overtakes Practice." The American Political Science Review 24, no. 4 (1930): 971-89. https://www.jstor.org/stable/1946754.
  • H. Ver Loren Van Themaat. "The Equality of Status of the Dominions and the Sovereignty of the British Parliament." Journal of Comparative Legislation and International Law 15, no. 1 (1933): 47-53. http://www.jstor.org/stable/753484.
  • Nathan, Manfred. "Dominion Status." Transactions of the Grotius Society 8 (1922): 117-32 . http://www.jstor.org/stable/742716.
  • Keith, A. Berriedale. "THE DEVELOPMENT OF COLONIAL SELF-GOVERNMENT IN THE NINETEENTH CENTURY." Journal of the Royal Society of Arts 56, no. 2883 (1908): 332-47.http://www.jstor.org/stable/41338132.
  • Leacock, Stephen. "Responsible Government in the British Colonial System." The American Political Science Review 1, no. 3 (1907): 355-92. https://www.jstor.org/stable/1944276.
• On the Spread of Christianity and Settler Colonialism:
  • Copland, Ian. "Christianity as an Arm of Empire: The Ambiguous Case of India under the Company, C. 1813-1858." The Historical Journal 49, no. 4 (2006): 1025-054. http://www.jstor.org/stable/4140149.
  • Greer, Allan. "Settler Colonialism and Empire in Early America." The William and Mary Quarterly 76, no. 3 (2019): 383-90. https://www.jstor.org/stable/10.5309/willmaryquar.76.3.0383.
  • Shoemaker, Nancy. "Settler Colonialism: Universal Theory or English Heritage?" The William and Mary Quarterly 76, no. 3 (2019): 369-74. https://www.jstor.org/stable/10.5309/willmaryquar.76.3.0369.
  • MacDonagh, Oliver. "Emigration and the State, 1833-55: An Essay in Administrative History." Transactions of the Royal Historical Society 5 (1955): 133-59. https://www.jstor.org/stable/3678901.
• On South Africa (or the Cape Colony):
  • Kuper, Hilda. "The Colonial Situation in Southern Africa." The Journal of Modern African Studies 2, no. 2 (1964): 149-64. http://www.jstor.org/stable/158816.
  • Porter, Andrew. "Britain, the Cape Colony, and Natal, 1870-1914: Capital, Shipping, and the Imperial Connexion." The Economic History Review, New Series, 34, no. 4 (1981): 554-77. https://www.jstor.org/stable/2595590.
  • Slater, Henry. "Land, Labour and Capital in Natal: The Natal Land and Colonisation Company 1860-1948." The Journal of African History 16, no. 2 (1975): 257-83. http://www.jstor.org/stable/180815.
• Other:
  • Osgood, Herbert L. "England and the Colonies." Political Science Quarterly 2, no. 3 (1887): 440-69. https://www.jstor.org/stable/2139184.
  • Beer, George Louis. ""British Colonial Policy, 1754-1765." Political Science Quarterly 22, no. 1 (1907): 1-48. https://www.jstor.org/stable/2140910.
  • Bryce, James. "Some Difficulties in Colonial Government Encountered by Great Britain and How They Have Been Met." The Annals of the American Academy of Political and Social Science 30 (1907): 16-23. http://www.jstor.org/stable/1010629.
  • Wilfley, Lebbeus R. "How Great Britain Governs Her Colonies." The Yale Law Journal 9, no. 5 (1900): 207-14. https://www.jstor.org/stable/782455.

Hope this list helps, and feel free to pm me or ask any follow-up questions regarding the sources as you see fit!

So, I'll try and provide a list of books, that will provide you with an appreciable understanding of the history of the Indian subcontinent between the period from roughly the 8th century CE to the beginning of the 19th CENTURY. This period saw the emergence of many vast Empires accross the subcontinent, and while these books won't be focusing on all of the them equally, this list of books largely covers the major powers of the region, the major political themes, social and military history and hopefully provides you with a chronological understanding of the Empires that emerged and fell in the time period concerned and shaped the region's history.

I'll also try and do my best to arrange these chronologically, in accordance with the Empires :

Before I list down more focused and specialised volumes on the time period we are trying to cover, it should be prudent to bring attention to a work which has provided an overview of the entire time period from the Tripartite Struggle to the Fall of the Mughal Empire and the rise of the Marathas to me time and time again and has been a source for reference and good reading namely A History of Medieval India by Satish Chandra, it's a work which covers the cultural and economic history of the Northern part of the Indian subcontinent during the Mughal Empire and Delhi Sultanate, it also pays attention to the Vijaynagar Empire and Bahmanids. It's extensive, ever useful and I would recommend reading this, before any of the volumes listed below.

This being said, now we may look at the more focused volumes :

THE TRIPARTITE STRUGGLE : THE PRATIHARA EMPIRE, THE PALA EMPIRE AND THE RASHTRAKUTA EMPIRE

1. The History and Culture of the Indian People Volume IV : The Age of Imperial Kannauj - RC Majumdar (Editor) : This fourth volume in the eleven volume series by under the general editorship of RC Majumdar, sheds light in the period from the beginning of the 8th century CE to the end of the 10th century and covers with great depth, the political history of the three Empires that came to dominate the subcontinent in this period, namely the Pratihara, Pala and Rashtrakuta. It also covers the achievements in literature and philosophy in the period, the changing paradigm of caste and social structures, and the history of Kannauj, which became a jewel in North India following the reign of Yashovarman. It is a comprehensive work and any reader should be able to understand the political and social reality of the Indian subcontinent in the time period concerned.

THE DELHI SULTANATE

1. The Delhi Sultanate : A Political and Military History - Peter Jackson : For a complete chronological political and military history of the Delhi Sultanate, this is a go to, it also covers that crucial period from the establishment of the Sultanate in the wake of the Ghurid conquests and death of Mohammed of Ghur in 1206, to the reign of Alauddin Khilji which the book by Majumdar listed below doesn't. During this period the Sultanate faced the existential threat of Mongol invasions and managed to defeat said invasions and thrive.

2. The History and Culture of the Indian People Vol VI : The Delhi Sultanate - RC Majumdar (General Editor) : Not surprisingly, this volume makes my list as yet another comprehensive work, which provides readers with a complete chronological political history of the Delhi Sultanate starting from the Khalji Dynasty and ending with Ibrahim Lodi's defeat at the 1st Panipat. It also discusses the contemporary and successor states that emerged during this period from roughly 1206 CE TO 1526 CE, such as the Gujurat Sultanate, the Bengal Sultanate, the Rajput states of Mewar and Marwar as well as the Vijaynagar Empire and Bahmanids and also pays attention to often ignored political entities of the time period, such as Orissa. It also goes into the social, economic, administrative, and religious developments and details concerned with the time period. A must read for a comprehensive understanding of the time period and a favorite of history buffs.

THE MUGHAL EMPIRE

1. Akbar The Great Mughal 1542-1605 - Vincent A. Smith : This detailed study of the life and career of perhaps the greatest Mughal Emperor to grace the Mughal Throne, provides a comprehensive account of his military campaigns, his ideology, his life and the social and economic conditions of the millions of lives over whom he would come to rule. The development of the administrative and revenue system, that would run the Mughal Empire for more than the next hundred years after Akbar's death, who would create institutions and systems that would be adapted and improved upon by the many successor states that would emerge from the disintegration of the Empire of his successors, also took shape during his career. VA Smith, does Akbar justice in his work and this is a book worth reading.

2. The Agrarian System of Moslem India and India at the Death of Akbar - W.H Moreland : These two volumes, both by WH Moreland, provide a detailed analysis of the revenue departments of various Muslim states that have existed in North India from the 13th century, down to the beginning of the 17th century, it also gives a detailed account of the agricultural sector, the social structures that supported and had come to define rural North India in this period, the lives and economic conditions of workers and peasants, their wages, their incomes etc. A must read for those interested in economic history and any readers looking for an elaborate answer to the question "How did the states or powers in this period extract revenue from the land owning classes, and what the economic conditions of the average citizens were like?"

3. A History of Aurangzib Vol I - Vol V - Sir Jadunath Sarkar : This 5 volume series on Emperor Aurangzib, whose reign began from the 31st of July, 1658 and lasted until 3rd of March, 1707, is essentially a history of around 60 years of India. This Emperor of the Mughal Empire, expanded the Empire to its zenith and at the same time, the problems and institutional decays that took root during his reign were directly responsible for weakening the Empire, for alienating it's majority Hindu subjects due to the discriminatory polices and actions of Aurangzib and creating the circumstances that eventually led to the downfall and ruin of the Empire. Sir Jadunath Sarkar, provides a detailed account of the history of this most controversial Mughal Emperor, he pulls no punches, and a study of these volumes gives one an understanding of the history of the subcontinent during the latter half of the 17th century, and gives the reader an insight, into the reason behind why one of the most military and economically powerful Empires of the 16th - 18th centuries, which in 1707 controlled nearly the entire Indian subcontinent, so abruptly seems to have lost it might and fallen from glory.