You know that old joke about how the “Holy Roman Empire” was neither holy, nor Roman, nor an empire? Here’s another one for you: the 1683-1699 Great Turkish War was neither great (especially if you were in the Ottoman army), nor “Turkish” (Turkish nationalism was still more than a century away). Cool, right? It also wasn’t a war–it was actually a series of them. Several European nations, including the aforementioned Holy Roman Empire (which at the time was controlled by the Austrian Habsburgs), Hungary (also controlled by the Habsburgs), Croatia (ditto), the Polish-Lithuanian Commonwealth, Russia, Venice, and a bunch of smaller partners all joined a new Holy League at the behest of Pope Innocent XI (d. 1689), and the Ottomans managed to entangle themselves in conflicts with each of them–the Venetians in Greece, the Russians in Crimea and at Azov, the Poles in Moldavia, and the Austrians in, well, Austria. This would have been a tough fight for the Ottomans to have won at their peak–and by the 1680s, they were no longer at their peak, though they weren’t a pushover either.
We’ve already mentioned a couple of the crucial battles of the Great Turkish War–the Battle of Vienna in 1683 kicked the conflict off and made for a pretty wrong-footed start from the Ottoman perspective, and the Battle of Mohács in 1687 cost the Ottomans a huge chunk of territory in eastern Europe. Those two battles, plus the Battle of Zenta in 1697 and the loss of Azov to Russia, were the major engagements of the war, and all went against the Ottomans. The result was the Treaty of Karlowitz, adopted on January 26, 1699, after two months of negotiations in the Habsburg town of the same name (the modern Serbian town of Sremski Karlovci). Karlowitz wasn’t a turning point in European history–the war was the turning point–but it does mark a milestone in the course of both European and Ottoman history, as it was the first treaty that the Ottomans were forced to conclude on European terms.
The Ottomans were forced to give up considerable European territory to the Habsburgs, territory that includes parts of modern Hungary, Serbia, Croatia, and Bosnia-Herzegovina. They lost Dalmatia (another part of modern Croatia) and the Peloponnese (in Greece) to Venice (though they got the Peloponnese back not long after), and parts of modern Ukraine and Moldova to Poland-Lithuania. Negotiations begun here and concluded in the Treaty of Constantinople (1700) ceded Azov to Russia (the Ottomans later got that back as well). But the symbolism of Karlowitz, the unambiguous acknowledgement that the power dynamic in the Ottoman-European relationship had leveled out or even shifted a bit toward the European side, was arguably more important than the treaty’s actual terms.
It’s common outside of Ottoman specialists to talk about the “decline” of the Ottoman Empire starting all the way back in the 16th century and fully manifesting with the Treaty of Karlowitz. The “What Went Wrong” school of mid-20th century orientalism embraced this framework because it made the eventual collapse of the empire the product of some immutable defect in the Muslim Mind or whatever, instead of another example of the normal historical ebb and flow between powerful nations. Among Ottoman specialists, however, the “decline theory” has been pretty well debunked. It’s kind of silly, if you think about it, to posit a roughly 350 year long decline phase. That’s more of a gentle descent, really. The more common academic view these days is to argue that Karlowitz marks a period of stagnation for the Ottomans, an “ancien régime” prelude to the modernizing 19th century, which transformed the empire into something very different than what it had been previously.
The Ottoman Empire was weaker in the 17th century than it was in the 16th century not so much because it was in decline, but because “weakness” can be a relative thing, and the rest of the Mediterranean had caught up to them. Yes, the empire struggled through a string of sultans, and even the occasional grand vizier, who weren’t exactly dynamic leaders–a decision in the mid 16th century to keep prospective heirs confined to the palace rather than letting then govern provinces and gain experience is usually blamed for this–but the imperial bureaucracy was so well-entrenched by this point that the machine of state hummed along regardless. Categorizing this as a time of stagnation fits the facts a lot better than calling it part of a massive, centuries-long decline. This is all to say that while the Ottoman defeat in the Great Turkish War shows, among other things, that the Ottomans weren’t able to fight a multiple front war against multiple European enemies, it doesn’t really show that the empire was swirling the drain.