Why No National College Build Option?

I have two cities who have both built libraries. But I can't see a build option for the national college.

Could it be because I have a Settler out moving around (but hasn't yet picked a spot to start a new city)?

I thought once each existing city has built a library the option automatically becomes available. Is there some research item I also need before I can build it?

Thanks!

Have you researched philosophy?

Philosophy.......................

OOPS... thanks

Don't plop the settler until the build is done.

If you plopped the settler, you will disabled national college building because you wouldn't have a library in your newest city.