How Was The Military Overrun?

I think this is an interesting topic, we never get a really big picture on how the military got overrun. The problem is if anybody dies they become a walker despite being bitten it makes it impossible to keep under control, people die everyday. Areas in lockdown would mean some people may die within meaning it could spread from the inside of protected areas. The army most likely would run out of ammo, we are not just talking about a couple of waves of zombies it would be wave after wave due to the zombies being attracted by noise. In the end they would just be outrrun and the soldiers would be outnumbered short term I think they would do well but overtime the supply issues would be clear.