what were the main causes of the santhal revolts?

The following points may help you:

a. Santhal revolt was against the oppressive British policies.

b.  The British through forest laws, restricted grazing , banned entry of villagers and tribes to reserved forests.  It lead to loss of customary rights

c.  The colonial collbarators purchased goods, particularly silk  made by santhals at a very low cost. They further sold the products at higher prices, making huge amount of profits.

d. In this way the traders indulged in massive exploitation of the tribals.

e. We may give example of silk, as to how santhal tribes were paid meagerly while the traders prospered.

f. Such was the problem  that Santhal tribal groups faced with the traders and East India company, who considered them as their enemies.

g. Likewise, moneylenders offered loans to tribals to meet their requirement for cash to produce goods , but they charged high rate interest from them. Thus, tribals faced the problem of repaying the loans and were burdened with huge debts. This became the cause for their terrible plight and misery.

h.  ​Santhals were  also recruited in Assam tea plantations. ​These tribes were recruited through contractors and were paid miserably low wages, they worked under terrible working conditions and were prevented  from returning home. All this led to revolt in 1855-56.