Border

Now borders no longer means of security

War is inside and every where

Very difficult to fight own people who take side of enemies

Our country  is divided in terms of language and culture. People do not want one single Bharatiya culture. This allows people from outside to come and exploit us. 

It's easier to target people in smaller groups.

Often regional interest is preferred over national interest

Common consensus on national basis is required to be built to plug the internal loophole just like we fence our borders for safety.