Chris Oates examines the show’s genesis in 1960s England, when the “British empire, like other European empires, was ending”:
In many ways, the show carried on the themes of Victorian youth literature: the Doctor is a fearless traveler; he encounters strange cultures and lands; he is stoic, sophisticated, and not without a few eccentricities. Give him a pith helmet and he could fit in perfectly with the entertainment of the past. Episodic adventure still sold, was still compelling, but with Doctor Who, the creators were confronted with the question of what happens to an empire-builder post-imperially? The question for the show’s creators was how to maintain the lucrative adventure structure of the past without the geopolitical foundation that it had required.
Their answer was to use the traits that were appealing about adventurers and were still permissible in a world where countries are not apportioned on a first-European-come, first-European-served basis. When inviting his companions to join him, he almost always asks if they want to see the universe. The stated mission is travel for its own sake. The Doctor is a tourist.