By 1878, which country was considered the biggest rival of the British Empire?

In the context of the late 19th century, particularly by 1878, Russia was viewed as the principal rival to the British Empire. This tension stemmed from several geopolitical factors, notably the competition for influence in Central Asia and the Balkans, which were crucial regions for both empires. The Russian Empire's expansionist policies created a significant concern for British interests, particularly in India, known as the "jewel in the crown" of the Empire.

The 1878 Congress of Berlin, which was held to address the territorial disputes resulting from the Russo-Turkish War, highlighted the competing interests of Britain and Russia in the region. Britain was wary of Russian expansion and sought to contain its influence, leading to heightened rivalries that shaped diplomatic relations in the years that followed.

While France and Germany were also important players in European geopolitics, the specific threats posed by Russian advances made it the most significant rival for Britain at that time. Italy was not yet unified and did not pose a comparable challenge to the British Empire in the same period.