During which conflict did Tsar Nicholas II's empire face significant challenges after a defeat?

Tsar Nicholas II's empire faced significant challenges after a defeat during the Russo-Japanese War. This conflict, which took place from 1904 to 1905, marked the first time a European power was defeated by an Asian power in modern history. The loss seriously undermined the credibility of the Russian military and highlighted the empire's weaknesses, including outdated naval strategies and military tactics.

The defeat not only led to significant territorial losses but also fueled domestic unrest and dissatisfaction with Nicholas II's leadership. It contributed to the 1905 Revolution, where widespread protests and strikes erupted, challenging the autocratic rule of the Tsar and ultimately leading to some political reforms, such as the establishment of the Duma (parliament).

In contrast, while World War I also posed enormous challenges for the Russian Empire, it began after the Russo-Japanese War, and the immediate repercussions of that earlier conflict set the stage for the turmoil that followed. The Crimean War and the Napoleonic Wars occurred earlier and involved different social and political contexts that did not directly involve Nicholas II's reign.