Punjab literally means "The Land of Five Waters" referring to the rivers: Jhelum, Chenab, Ravi, Sutlej, and Beas.
British had won entire India by 1818, after Maratha Wars.
Punjab alone stood as an independent country till 1845 before it lost the First Anglo Sikh War.
After 1849, after the Second Anglo Sikh War, Punjab was merged into British India.
In total, Punjab had an area of approximately 357 000 square km about the same size as of today’s Germany, being one of the largest provinces of the British Raj.
First Division of Punjab: The 1947 partition of the Subcontinent divided Punjab into two parts – the West Punjab, belonging to Pakistan and the East Punjab, which became part of India.
Another Division of Punjab: PEPSU was merged to form United Punjab in 1956. On 1st November 1966, United Punjab was divided into Punjab and Haryana. The mountainous regions of Punjab were merged with Himachal Pradesh, a union territory at first. Himachal Pradesh became a state in 1971.
The total area of Today’s Punjab is only 50,362 square kilometers about the same size as of South American Island Costa Rica