Why did the Ottoman empire decline technologically against Europe even if it did not enter isolationism like China or Japan?

For the most part, it didn’t. Excluding brief periods like the first decades of the 19th century, technology was not the chief reason for the Ottoman Empire’s military misfortunes, nor its economic woes. Rather, Ottoman military effectiveness and economic development waxed and waned throughout the long 19th century, with both successes and failures.

At the turn of the 19th century, Ottoman forces were unquestionably outdated, weighed down by the institutional inertia of the praetorian Janissary corps. The corps’ purge in 1826 triggered a military modernization along Western lines, and from that point forward, obsolescence of technology or ideas ceased to become the chief problem for the Ottoman army.

Their new problems were harder to solve – they were constantly at war with Russia, a country with many times more people, and lacked the funds to properly equip and motivate a large army. The Ottoman army in 1905 had more than a million soldiers but spent only £14 per soldier. In contrast, the German army spent £60. Such attempts to save money resulted in an army of underpaid, under-equipped troops who had no motivation to stay and fight.

In spite of these issues, the Ottoman army achieved not inconsiderable success. In the Crimean War, a conflict mired by incompetence on all sides, the performance of general Osman Pasha was outstanding. In 1878, the Ottomans had alone highlight during the Siege of Pleven, where they inflicted heavy casualties on the Russians. The Ottomans were fully capable of defeating minor powers, triumphing over Serbia in 1876 and Greece in 1897. In the First World War, Ottoman forces famously held back a massive Anglo-French landing at Gallipoli and encircled the British at Kut.

When evaluating Ottoman military performance, it is helpful to abandon Orientalist tropes about the empire not being “modern”, but rather to see the Ottoman Empire as equivalent to other multi-ethnic and economically peripheral empires, chief among them Russia. The problems of the Ottoman military were largely the same as those of the Russian military – a budget not suited to its size, illiteracy among enlisted ranks, and a neverending game of “catch up” to the West. As in Russia, the fortunes of the Ottoman military rose and fell with politics – the force saw a sharp decline after the accession of Abdul Hamid II, who forbade land or naval maneuvers since they could be cover for a coup.

The empire’s economic fortunes were just as uneven. The Ottoman Empire embraced a version of the laissez-faire economics that was mainstream at the time, and, most decades, spent less than 20% of its budget on economic development.

That said, Ottoman taxes were generally less than 16% of the country’s GDP, so this in no way meant that the majority of the country’s resources were being directed towards war and debt repayments.

The Ottoman Empire did see economic development during the 19th century, with numerous railroads and industries built. While it was forced to invite foreign firms to modernize its financial and industrial sectors, the economic effect of these firms was not as broadly negative as historians once imagined – the much-maligned Ottoman Public Debt Administration, for example, was actually a much more efficient tax collection authority than the previous Ottoman revenue office.

The fate of states is not just constrained by ideas but resources. By all indications, the Ottoman government had all the right ideas after the Auspicious Incident of 1826, but the country was too poor and its population too small and diverse (in an age of rising nationalism) to save the great majority of its territory from foreign and domestic enemies.