HODGES: I don't think Russia is bottomless pit of manpower. Many of the youngest ones are either dead or have fled the country.
Year ago, I heard Putin complaining there weren't enough people to work in the factories. Well, no shit, because they're all dead, gone, or deployed.
The vast majority of Russian troops come from well outside St. Petersburg and Moscow. They come from poorer regions of Russian Federation, where people are happy to take signing bonuses to join the army.
Kremlin seems to have studiously avoided any mobilization that would require pulling people from Moscow and St. Petersburg, because it would then be impossible to hide the scale of the disaster.