The Cause of historical importance of Mujibnagor.

The Barbarous Action of Pakistan Army
The Bengali Language Movement of 1952 was the first sign of friction between the east & west Pakistan. Dissatisfaction with the central government over economic and cultural issues continued to rise through the next decade, during which the Awami League emerged as the political voice of the Bengali-speaking population. Sheikh Mujibur Rahman (Mujib), was jailed; he was released in 1969 after an unprecedented popular uprising. In 1970, a massive cyclone devastated the coast of East Pakistan, killing up to half a million people, and the central government responded poorly. The Bengali population's anger was compounded when Sheikh Mujibur Rahman, whose Awami League won a majority in Parliament in the 1970 elections, was blocked from taking office.
After staging compromise talks with Mujib, President Yahya Khan arrested him in the early hours of 26 March 1971, and launched Operation Searchlight, a sustained military assault on East Pakistan. Yahya's methods were extremely bloody, and the violence of the war resulted in many civilian deaths . Chief targets included intellectuals and Hindus, and about ten million refugees fled to neighbouring India. Estimates of those massacred throughout the war range from three hundred thousand to 3 million.

Before his arrest by the Pakistan Army, Sk. Mujibur Rahman formally declared the independence of Bangladesh, and directed everyone to fight till the last soldier of the Pakistan army was evicted from East Pakistan. Awami League leaders set up a government-in-exile in Calcutta, India. The exile government formally took oath at Badyonathtala (Now Mujib Nagar) which was mainly a big mango grove located at 12 kilometers away from Meherpur town  in Kushtia district of East Pakistan on 17 April 1971, with Tajuddin Ahmad as the first Prime Minister.

Bangabndhu Sheik Mujibur Rahman laid down an order to preserve the mango grove as a site of historical importance on 31 August 1973 after Bangladesh had earned its freedom. This historical place is now a popular picnic Spot.