C3 war issue

my country cant occupy a country even though enemy war index has been reduced to 10 cant go more than that all cities,capital,corps,enemy uniys and forts has been destroyed still cant occupy enemy country please help guyz

No one can help unless you tell us what world and what country this is regarding.

Invade the country with land forces and then attack town or county

Invade indeed.

You cannot reduce the index any more by air attacks.
you need to occupy some of the country to reduce the index to zero.