Pakistan used to be part of India but Pakistan split off when India got independence because the Muslims of Pakistan did not want to live in a country where they would be a minority and possibly ruled by Hindus from India. Mahatma Gandhi opposed the partition, saying it would create conflict between Indians, who he felt should be united in one nation.
After the partition, Pakistan and Bangladesh were one country, known as Pakistan. What is now known as Pakistan was called West Pakistan, and Bangladesh was called East Pakistan. The two Pakistans later fought in a civil war, and Bangladesh became independent.
There used to be a fairly large and ancient minority of Hindus (an estimated 17% of the population) in Pakistan but over the years since the start of Muslim rule most felt uncomfortable with the elements of Sharia Law and Jizya in the society and moved out. Now Hindus comprise only 2% of the population. Since 1970 Hindus in Pakistan have been treated worse than Muslims or Christians. Many converted under pressure to Islam or Christianity.
Neoconservative warmongers who never served a day in uniform use Pakistan to cause fear by saying "Oh no the bogeyman, Osama bin Laden, is hiding there". Fortunately, Barack Obama killed him and Republicans can sleep peacefully at night.