1. Revolt is a rebellion caused against someone caused for some good reason.
No, not all revolts are necessary as some revolts are started to capture one's empire,fort,etc. However, some revolts like Revolt of 1857 was a necessary one.
2. The impact of Revolt of 1857 was :
i. After the Revolt of 1857, the Government of India Act was passed and the British East India Company was abolished and India passed directly under the British crown.
ii. The new office of the Secretary of the State was created.
iii. The powers of the Government-General were enlarged and the office of the Viceroy was created in its place.
iv. The Proclamation abolished the Doctrine Of Lapse and the annexed territories were returned to the princes.
v. Queen Victoria promised to look after the welfare of the people.
Yes, the Revolt would be called the First War of Independence because it was the first time that it created the hope of Independence and encouragement among the masses.
3. The Ban on Sati act and Widow Remarriage had little effect as the Hindus constituted majority of the population and since they were orthodox they soon started to disobey the acts.
4. British East India Company enlarged their territories by the Doctrine of Lapse, which included that if a king did not have a heir to the throne the kingdom would be passed directly to the British.
The other steps were the money lending system,example: Ryotwari and Mahalwari Settlement.
5. The causes for decline of Mughal Empire was:
i. Weak successors of Aurangzeb- The successors of Aurangzeb were weak and inefficient and they were pleasure-loving and could not manage such huge empires. The administration became powerful and controlled the rulers like puppets.
ii. Wars of Succession- After the death of a Mughal Emperor, many of his relatives laid claim to the throne. This resulted in wars of succession which weakened the empire and made it unstable.
iii. Failure of the Mansabdari System- The Mughal mansabdars collected revenue, with which they maintained large armies as per their ranks. After Akbar, the mansabdars grew in number and there were not enough jagirs available. This led to corruption in Mansabdari system. The Mughals did not have a navy and they did not adjust with times.
iv. Jagirdari Crisis- The mansabdars grew in number and there were not enough jagirs available. This led to corruption in Jagirdari system.
v. Foreign Invasions- Nadir Shah and Ahmad Shah Abdali took advantage of the weak successors of Aurangzeb. Nadir Shah took away the Peacock Throne and Kohinoor Diamond. This destroyed the Mughal dynasty.