Yeah, I know what little they showed of the military fighting the zombies in The Walking Dead
(hence my remark about "not showing it in any detail"), just as I knew what was in the novel of World War Z
when you told me everything that happened in that too. Explaining things that I've already seen and read too and that don't alter my point in any way is not really useful.
The point is that how the zombies took over the world in TWD
is not really important to the story. It's just something that had to happen in order to get to the story they really wanted to tell, which is that of a small group of survivors learning to cope in the aftermath of this massive ongoing tragedy.