The 1683 Siege of Vienna between the Ottomans and Habsburgs.
Mehmed IV wanted to live up to, and even surpass, the legacy of his forefather Mehmed II, who had secured the Ottomans' inheritance to the Roman Empire through his conquest of Constantinople. So the current Mehmed decided to target Vienna--but Emperor Leopold dismissed these threats...
The siege presses on from its initial active resistance phase to the long, routine drudgery of survival on the inside and elaborate defense building on the outside: earthworks and revelins designed by Georg Rimpler. Meanwhile, the Ottomans prepared to attack via gunpowder prepared inside mining tunnels.
Leopold knew it was time to get the Holy Roman Empire involved if he wanted to keep Vienna, but it wouldn't be as simple as asking for a favor. Charles of Lorraine and Sobieski of Poland would be the ones to lead the charge on the battlefield against the Janissaries.