The Western civilization was forged by the horsemen of the apocalypse: Goths, Huns, Vikings, the Crusades, Mongols, and Black Death.
From the devastating nomadic invasions and the failure of the crusades, the Europeans developed the appetite for invading, massacring, conquering, and plundering. The Black Death killed between 30 to 60 percent of the European population in the fourteenth century. The decadent political elite of Europe was finished, the political order collapsed, and power went into the hands of a new class of ambitious, aggressive, and adventurous people who wanted to use the tactics of the nomadic Goths, Huns, Vikings, and Mongols to conquer the world. They wanted revenge for the failure of the crusades.
The philosophy of the Classical Age (Ancient Greece) has played a minor role during the Age of Imperialism. There was no philosophical motivation behind Imperialism, which was a nomadic, militaristic, and vengeful enterprise. To create a mountain, you don’t need a stable geology—you need a massive earthquake. To forge a world-conquering civilization, you don’t need philosophy—you need the horsemen of the apocalypse.