Not civil war, but South Indian states are economically at a disadvantage remaining part of India. Plus the invasion of North Indians into the South hasn't been welcomed because they're enforcing Hindi upon them.
If I'm Pakistan, I'd fan the flames a little bit. An independent South India would be beneficial to both. South India becomes the powerhouse it was destined to become without the poor North dragging it down, plus they'll have no territorial disputes or hostilities against us.
North India will essentially become Somalia v2.0.