An addendum to the recent post on Mechanised/infantry mix in NE Europe:
First have a look at this.
It's similar with infantry. The need for infantry corresponds with the terrain better than with the quantity of manoeuvre battlegroups in the theatre of war.
This is another reason why the old quest for an optimal ratio between mounted (mechanised/tank) and dismounted (infantry) strength is misleading.
Then there's the large repertoire of missions, which by their nature have different optimal ratios for organic mounted and dismounted strengths.
Another reason is that attrition (both due to wear & tear and due to hostile actions) may very well be different (and largely unpredictable) among mounted and dismounted combat forces.
The employment of dismounted line of sight combat strength is almost inevitably slow at the unit level and above. A platoon may dismount, investigate a farming compound in less than five minutes and proceed, but deployments of whole infantry units would typically be much longer. The entire way of thinking about terrain and time changes with an infantry focus.
The objective of excellence was and is to switch between mounted and dismounted action back and forth very quickly depending on need, but actions are much slower the more needs to be accomplished by dismounted forces. Long story short: Infantry slows tanks down.
A certain infantry component accompanying tank forces makes much sense (even more of it than we have nowadays with the IFV concept), but on the corps level it's much more sensible to separate infantry-centric battlegroups (which should have a mission for a certain area) and manoeuvre battlegroups, which need be able to move 50+ km within two hours of receiving the order or recognising the need by themselves, 24/7.
I'm thus treating the infantry less as manoeuvre forces on the corps HQ map, while considering them as manoeuvre forces on the battalion HQ map. This scale fits to their actual mobility. That's why I see a strong correlation between the theatre of war's terrain (size and structure) and the need for infantry strength.