Jonah’s military guy weighs in: “The reasons are pretty simple, really. Prior to WWI, we didn’t need large installations. You could train the infantry, cavalry, and artillery on the parade grounds.
“The expansion of the battlefield caused by machineguns, small bore smokeless powder rifles and indirect fire artillery changed tactics to more dispersed formations covering far greater distances, and the maneuver and control of forces shifted dramatically.
“Most of the big posts in the South we established in WWI, with some in WWII, or which were reopened in WWII.
“The South was chosen for many reasons, most of them economic. It was less densely settled, it was therefore cheaper to acquire the land, and you had
larger tracts of land that were clear of significant urban areas. There was a good mix of hilly, forested and clear land, as well, with good rivers etc. Labor
in the areas was cheap, building supplies plentiful, and the climate more benign, a consideration when trying to get things established. Try expanding Fort
Stewart Georgia in January 1942, vs. Fort Snelling, Montana in January 1942, for example.
“The southern installations were also generally closer to the ports that were going to be used to ship the troops overseas, and were adequately served with rail service to get the heavy gear the units would need to train to those locations.
“And when you wanted to conduct large-scale maneuvers, like the Louisiana Manuevers (which took place in several states) the overall dislocation and
inconvenience to locals and disruption of commerce was less in the southern states.
“Those same reasons still militate for keeping the bases we have there. You could make arguments about closing Fort Riley and Fort Carson, because they are in the interior, etc, but the reality is we don’t dare give up large maneuver spaces anymore – because absent a war the scale of WWII, we’re never going to be able to get parcels of land that size again.
“What was sufficient dirt to train an infantry division in WWII is barely large enough for a modern mech battalion.”