It was felt that the Indian Mutiny in 1857 had revealed weaknesses in the political relations by which the sub-continent was controlled, so the sovereignty of India was transferred to the crown and the governor-general was replaced with a viceroy. The assumption of the title “Emperor of Germany” by Kaiser Wilhelm I in led Queen Victoria to ask Gladstone why she had no such title. Gladstone objected that the title was without precedent in British history. When Disraeli became Prime Minister in 1874 he was ready to oblige and early in 1876 the Royal Titles Act (39 & 40 Vic. c. 10) conferred on Victoria the title of Empress of India. The title came into force on January 1 1877.
Editors. "Queen Victoria proclaimed Empress of India". The Literary Encyclopedia. First published 01 January 2007
[http://www.litencyc.com/php/stopics.php?rec=true&UID=1700, accessed 23 January 2017.]