The Polish Lithuanian commonwealth was once one of the largest and most powerful nations in Europe, with a unique military system, and many enemies.
In 1648, a massive Cossack revolt almost brought the Commonwealth down. This revolt was in itself a fascinating conflict, with many Cossack units deserting the Polish military to join the revolt, intervention from the Crimean Tarters, and many campaigns and great leaders.
Other wars followed on this one, wars with Russia, Sweden, which almost conquered the commonwealth, and The Ottoman empire, wars which saw Poland rebound time after time, culminating in the relief of Vienna by Jan Sobieski as the last Ottoman invasion of Europe was crushed. Yet only a few years later, the Commonwealth collapsed into civil war and division, and lost much of its land, eventually all of Poland was conquered and annexed by its enemies.
None of these fascinating wars, which featured very different military systems in conflict, have ever been covered. This system would be ideal for it.