Indian annexation of Hyderabad

The Annexation of Hyderabad (code-named Operation Polo) was a military operation launched in September 1948 that resulted in the annexation of the princely state of Hyderabad by India, which was dubbed a "police action". At the time of partition of India in 1947, the princely states of India, who in principle had self-government within their territories, were subject to subsidiary alliances with the British, which gave control of external relations to the British.

Source: Wikipedia — Indian annexation of Hyderabad (CC BY-SA 4.0)