An Ottoman Empire fighting alongside the Allies would leave a supply route to Imperial Russia through the Dardanelles. That route would not be perfectly placed for every Russian front. The counterfactual nevertheless treats it as close enough to make a material difference. Ottoman alignment therefore affects the war through access and supply as well as through the forces directly engaged.
Notable Point · 2:03:19-2:03:40
An Allied Ottoman Empire opens a route to Russia
Keeping the Dardanelles open to Allied supply gives Ottoman alignment a logistical consequence for Russia.