To where exactly is supply traced? I assumed back to a friendly capital, but ...
In my first game, playing the CP against the AI, I pursued a conventional WWI strategy: hold with the Austrians against the initial Russian attack, then after the West Front has stabilised, launch simultaneous offensives south from Konigsberg and northeast from Lemberg, to meet near Brest Litovsk.
Now, given the slow pace of advance in WWI, nobody expects this grand pincer to actually trap much of the Russian army in Poland. Since it is so obvious what the strategy is, the intention is merely to force the Russians to evacuate Poland before the pincers snap shut, so that Polish territory can then be swept up cheaply.
Only, the AI didn't see it that way. It's mid-1916, and three-quarters of the Russian army is now cut-off in Poland by a cordon about two or three hexes wide running from Konigsberg to Brest Litovsk to Lemberg. I assumed that it was now all over bar the shouting. I imagined that surrounded, the Russian army would be out of supply, unable to Refit HQs or corps, and that their Readiness would quickly degrade to close to zero.
Not a bit of it. The forces inside the encirclement are launching powerful counterattacks to reopen a supply line every second impulse, suggesting their HQs are being restocked and that their Readiness has not been degraded. So to where does the AI permit players to trace supply? Surely not Warsaw?
I notice that obscure places like Erzerum and Yerevan offer 100% supply, while all surrounding hexes are about 37%. This suggests the very nasty, and utterly unrealistic, possibility that the game has been programmed so that units can draw supply from any friendly city, in which case attempting a grand envelopment is a complete waste of time.
In the final impulse of May 1916, suddenly all German and Austrian supply percentages shrank across the map. Some places that had been about 90% dropped to less than 20%. Berlin itself fell to 96% and Vienna to 91%. But the Turks were completely unaffected, sporting 100% all over the place still. Then equally mysteriously the following turn all supply percentages returned to normal levels.
Although both Germany and Austria were close to the first Exhaustion event, neither tipped over that turn, so that was not the cause of it. The only thing that happened was that the CP achieved Trench 3.