I think ultimately the real weapon of mass destruction will be long-range drones the size of a DJI drone, each holding a small but extremely powerful explosive.
And then send millions of them, with specific single targets. Each AI controlled to target single weakpoints in buildings, bridges, or even specific people. You can't stop a million of them even with EMPs because you can just end a million more. You can destroy entire cities with a technology like this. If each drone costs $10,000 and you send a million of them that's only $10 billion for a war and complete destruction of your enemy.
And then send millions of them, with specific single targets. Each AI controlled to target single weakpoints in buildings, bridges, or even specific people. You can't stop a million of them even with EMPs because you can just end a million more. You can destroy entire cities with a technology like this. If each drone costs $10,000 and you send a million of them that's only $10 billion for a war and complete destruction of your enemy.