Particularly for electric cars - you have very inflamable lithium batteris, which when spiked very hard (by something sharp), so multiple layers short circuit and well short circuits leads to fire. But batteries are at the bottom of the body, with few easily exposed areas (otherwise they would be at risk of explosions all time). I do not know what people are doing exactly, but you can use a crowbar like thing to hit the beneath posterior, until you expose the battery, and then 1 or 2 hits can do it, or you can skip this and use a smaller conventional explosive.
I would like to add this - I do not condone arson. Even if anyone wants to protest - this is not the way to do it, unless you burn your own stuff, then you are only harming environment. What i wrote is purely for educational purposes.
One thing that would quickly start to happen is a lot of the smaller countries would either be forcefully taken over or be quieted down. Most countries have neighbours they do not share good relations with - and with nuclear armament - bigger of 2 could easily pose nuclear threat and have a much bigger say in their arguments. This could mean taking over contested/disputed lands or some kind of minearl deals being forcefully signed. Soon the total world country count would start to decrease purely because of this (annd would actually accelerate until a point where most countries would form coallitions with some nuclear power and sum total of power on both (or all sides in general) be roughly comparable such that no one poses a greater threat to another and not have an equal threat back at them.