Weather and tactical errors aside... How much of a role did Russian Nationalism play in Stalingrad and who/what was inspiring the Russians to put up such a big defense and why?
The Germans were targeting the oil fields of Baku, that was the objective and in order to get there they had to take Stalingrad; without fuel the Russian tanks and planes could not have worked;
In turn the allies too were targeting German fuel production; namely the Leuna works that produced synthetic fuel and Romanian oil fields in Ploieşti during the oil campaign / operation Tidal Wave.