Question

How did the mutiny become a popular rebellion

Answer 1

Over time, different Indians from all walks of life began to view the British as their common enemy.
They became united to rise against the British, and in May 1857, a massive rebellion started that threatened the company’s very presence in India.
From Meerut To Delhi

On 29 March 1857, a young soldier named Mangal Pandey was hanged to death for attacking his officers in Barrackpore.
The sepoys, most of whom were Hindus and Muslims, refused to do the army drill using the new rifle cartridges which they suspected of being coated with the fat of cows and pigs to destroy their religions.
Determined to bring an end to the company’s rule. the sepoys rushed from Meerut to Delhi. 
As the news of their arrival spread, regiments stationed in Delhi also rose up in rebellion. They killed several British officers, seized arms and ammunitions, and set buildings on fire.
Finally, they met the Mughal emperor Bahadur Shah Zafar and proclaimed him as their leader.
The Mughal emperor also got support from the rulers and chiefs of the country, and together they rose against the British power; people were convinced that the Mughals would make better rulers than the British.
The Rebellion Spreads

After the British were routed from Delhi, there was no uprising for some days. Then, a spurt of mutinies began, and regiment after regiment mutinied and took off to join other troops at nodal points like Delhi, Kanpur and Lucknow.
After them, the people of the towns and villages also rose up in rebellion and rallied around local leaders, zamindars and chiefs who also were desperate to establish their authority and fight the British.
Nanasaheb, the adopted son of the late Peshwa Baji Rao, gathered armed forces, expelled the British garrison from his city, and he declared that he was a governor under authority from the Emperor of India Bahadur Shah Zafar.
In Lucknow, Birjis Qadra, the son of the deposed Nawab Wajid Ali Shah, was proclaimed the new Nawab; his mother Begum Hazrat Mahal took an active part in organising the uprising against the British.
In Jhansi, Rani Lakshmi Bai joined the rebel along with Tantia Tope, the general of Nana Saheb.
New leaders came up like, Ahmad Ullah Shah, a maulvi from Faizabad, came to Lucknow to fight the British.
In Delhi, a large number of ghazis or religious warriors came together.
Bakht Khan, a soldier from Bareilly, took charge of a large force of fighters who came to Delhi, and became a key military leader of the rebellion.
In Bihar, an old zamindar, Kunwar Singh, joined the rebel sepoys and battled with the British for many months.