On August 15, 1947, two independent states were established on the map of the world, India and Pakistan. The Muslims of the Sub-Continent got Pakistan while the Hindus got India as a result. However, the third largest community of the region, the Sikhs did not get any thing substantial but just hollow promises made by the then Hindu leaders, Nehru, Mahatma Gandhi and Patel. These promises were never materialized.
There is no doubt that the Hinduism was able to amalgamate all the religions of the subcontinent throughout the centuries fairly successfully but not Islam. The Muslims were often called as Muhammadan Hindus both by the Hindus and the British after the British conquered India. Even in Mughal era, several attempts were made to mix the two religions by taking some beliefs from Islam and others from Hinduism, but to no avail. Islam kept its unique cultural and religious identity despite all the adversaries.
However, that was not the case with the Sikhs. The Hindu leaders during the pre-partition were able to make the Sikhs realize that they were a part of Hindu religion. So, they should unite forces with the Hindus to get independence. This served their purpose quite well especially during and before the partition of the Sub-Continent as they had to show a much larger community of the Hindus to the British and the world. The Hindus simply wanted to show their majority in the region which they succeeded and got a huge land area which is now called India.
After getting independence, Nehru, the then Prime Minister of India, made sure that the Sikhs migrating from the Pakistani part of Punjab should be settled in different parts of the India instead of living in East Punjab only. This way, India was able to successfully change the demography of the Punjab province where now, more than 50% of people are non-Sikhs.
As a consequence of the partition, the Sikhs lost some of their most important places of worship in the West Punjab (now in Pakistan) which became a part of Pakistan from where most of the Sikhs had migrated to the East Punjab in the newly formed state of India. They lost Nanka Sahib, the most important seat of the Sikh religion, Ranjeet Singh Marhi, Saccha Souda, Kartarpur and Gurdawara Punja Sahib in Hassan Abdal. all located inside the areas controlled by by present-day Pakistan.
In the early 1980s, they started a freedom movement called Khalistan Movement. However, as they did not have much political will and force to get significant concessions from their Hindu rulers of India for the Sikh community living in India, the movement was brutally suppressed by the Indian Government in 1984. The East Punjab was further divided into three different provinces namely Punjab, Haryana and Himachal Pardesh. This significantly weakened the Sikh community in India, thus leaving them almost powerless in the country.