National Defense

I am a simple man, and complex historical events elude my feeble grasp. So I'm confused by the following:

In the 1950s, Eisenhower pushed for the interstate highway system on grounds of national defense. (He had been impressed with the German highway system during WWII and its effectiveness for transporting materiel.) So the U.S. built the interstate system, and auto companies built and sold lots of lots of cars to drive on them, and oil companies sold lots and lots of gas for the cars.

In the early years of this decade, some people who were mightily pissed off about the U.S. meddling in their oil-rich lands committed some acts of horrific violence on some prominent American targets. The loss of life was, by U.S. standards, staggering.

Now, what was that about building highways in support of national defense?