Russia wants the NE province for its dominance. Continuing the Persia game, the Austrians and Ottomans were embroiled in a long war that went badly for the Austrians early on but they edged back and a Persian invasion once the army was up to 30K+ again really helped them - they got 50 Warscore, Persia 40 and peaced out after capturing every city in Ottoman Asia except Kars and Rhodes (Constantinople was protected from our crossing by the Turkish fleet, but repeated attempts on both ends of the straits got a division through which then found Constantinople with a very large garrison. The Turks in desperate condition with almost everything overrun, in 1810 after several years of war they yielded 9 provinces in the east including salients pointing west at Erzerum in the north and Aleppo almost at the Med as a future choke point. Can't build in the non-core regions, but this did double manpower flow and provides a nice geographic cushion against invasion.
Ideas chosen to 1810 were foot soldier boosters Volley Fire, Assault Column, Platoon Fire, Mixed Order, and finally March to the Sound of the Guns which sounded useful when spread out over the OE. This yielded a nice 120% or so quality which was a large edge over the Turks near 80%.
Elsewhere in the world there were several convoluted wars, with France holding chunks of Portugal and swathes of Germany including a lot of Prussian lands, having lost land dominance and then recovered it.
Not much chance for diplomacy, other than building relations with Austria, which also enjoyed the benefit of the Persian second front.
In multiplayer I imagine Persia, if secure from Russia and the OE, could do something with its army.