it could not become a mass party because in order to do so it was first necessary to overthrow the old parties and it was possible to overthrow them only by an irreconcilable struggle, by a merciless exposure of their bourgeois character.

Make this proper case.
It could not become a mass party because in order to do so it was first necessary to overthrow the old parties and it was possible to overthrow them only by an irreconcilable struggle, by a merciless exposure of their bourgeois character.