Imagine a theoretical scenario where an artillery 3.5m across and 150m long is built underground (its possible, according to a science magazine). A 20 ton tungsten shell is fired into orbit and strikes a target thousands of miles away. Since the escape velocity is 30000km/h, assuming that the shell does not lose speed during reentry, the speed would be 8333m/s. Here is the scary part. According to the equation ½mv^2, the KE would be 10 terajoules. That is almost as powerful as the hiroshima bomb. But if a hostile country (say Iran) were to fire shells like that as if it were artillery, I don't see a difference between this and the cold war.