A country's capital and a country's most famous city are two different jobs, and a striking number of governments have deliberately kept them apart. Washington, D.C. isn't America's biggest city. Canberra isn't Australia's. Brasília isn't Brazil's, and it was built from nothing specifically so that no existing city would end up holding that job. None of this is a coincidence, and it isn't really about picking a winner — it's a pattern with its own logic, and once you see the logic, a lot of the world's national capitals stop looking like odd trivia answers and start looking like deliberate choices.
A capital is a legal designation, not a popularity contest
Being a country's capital is a specific, formal status — the seat of national government, usually fixed by a constitution or founding law — and that status answers a different question than "which city is biggest" or "which city is most famous abroad." A country's economic centre, its cultural centre, and its political centre can easily be three different cities, and there's no rule anywhere that says they have to line up. Once you stop expecting capital and biggest-city to be the same thing by default, the exceptions stop looking like exceptions.
Plenty of capitals were built, or chosen, specifically to avoid favouring an existing city
A recurring reason a capital isn't a country's most famous city is that it was never supposed to be: it was picked, or purpose-built, precisely so that no existing rival city would get the political prestige of hosting the government. Washington, D.C. sits on land carved out as neutral federal territory, a compromise between competing regional interests rather than a reward to Philadelphia or New York. Canberra exists at all because Sydney and Melbourne couldn't agree which of them should be capital, so a new city was planned roughly between the two. Brasília was built inland specifically to shift national attention away from the coast and toward the country's interior. In each case the "obvious" answer — the biggest, richest, most internationally recognisable city — was the one thing the decision was designed to avoid.
Capitals also move, and a country can legally have more than one
A capital isn't necessarily permanent, either. Governments relocate their seat of power for reasons ranging from decentralising development away from an overcrowded coastal city, to putting distance between the government and a colonial-era capital after independence, to reducing a single city's outsized political weight — Nigeria's move from Lagos to the more centrally located, purpose-built Abuja is a well-known modern example. Some countries go further and split the job formally: South Africa runs three official capitals at once, one for the executive branch, one for the judiciary, and one for the legislature, precisely so that no single city holds every lever of national power.
What we're still unsure about
Which city legitimately counts as a state's capital isn't always a settled question, either. Recognition of a capital is decided government by government rather than by any single global authority, so the same city can appear as the plainly agreed capital on one country's maps and as a disputed or unrecognised claim on another's — and in a handful of ongoing cases, that disagreement has lasted decades with no resolution in sight. Geographers and political scientists can describe exactly how these disputes work, but settling any individual one is a diplomatic question, not a geographic one.
This sits across all nineteen regional topics in World Capitals, one of five domains in Geography, one of seventeen subjects the app can quiz you on.