Yes, I am serious. Invading armies would be too spread out at a distance for the nukes to have the desired effect. Once they are massed in the border area they can be taken out hundreds of thousands at a time, but at great risk of contamination.
Decapitating the leadership is an option, if you can find them. They certainly won't be sitting in HQ in their capitol city or a military base waiting to be vaporized!
“Invading armies would be too spread out at a distance for the nukes to have the desired effect.”
Why would an army invade Israel? The military has missiles now. Even Iran is counting on missiles to destroy Israel, and they can mass an army inside their own borders close by. Why go to all that trouble when a few missiles is all it takes?
No invading army splits their forces. General George Custer tried that.