The correct answer is option 'A': the Indian Princes kept fighting each other. Let's explain this answer in detail:

Political Fragmentation and Power Struggles:
During the period from 1757 to 1849, India witnessed a lack of peace primarily due to the constant fighting among the Indian Princes. This era was characterized by political fragmentation and power struggles among the various regional rulers and princely states in India.

1. Rise of Indian Princely States:
After the decline of the Mughal Empire, several independent princely states emerged across the Indian subcontinent. These states were ruled by local Indian rulers, known as Princes or Rajas, who aimed to expand their territories and establish their dominance.

2. Ambitions and Conflicts:
The Indian Princes were driven by their ambitions for power, wealth, and control over resources. As a result, they frequently engaged in conflicts and wars with each other to assert their authority and expand their territories. These clashes often took the form of battles, skirmishes, and sieges.

3. Lack of Central Authority:
With the decline of the Mughal Empire, there was a lack of a central authority that could enforce peace and maintain order across the region. The absence of a strong central government created a power vacuum, allowing the Indian Princes to engage in territorial disputes and power struggles without any effective mediation.

4. British Intervention:
Amidst the ongoing conflicts among the Indian Princes, the British East India Company gradually established its presence and influence in India. Taking advantage of the political fragmentation and weak central authority, the East India Company expanded its control over various regions, further exacerbating the conflicts among the Indian Princes.

5. British Policy of Divide and Rule:
The British adopted a policy of "divide and rule," exploiting the existing rivalries and conflicts among the Indian Princes to maintain their control and suppress any potential uprising against their rule. By supporting one Prince against another, the British exacerbated the tensions and perpetuated the cycle of violence and instability.

Conclusion:
In summary, the lack of peace in India from 1757 to 1849 can be attributed to the constant fighting among the Indian Princes. Their ambitions for power, weak central authority, and British intervention all contributed to the ongoing conflicts and political instability during this period.