Not every capital is the largest city
Washington, Brasília, Canberra, Ottawa, Ankara and many other capitals show why “largest city” is a poor shortcut. Some capitals were selected as political compromises; others were purpose-built or moved inland. Learning the reason behind an unusual capital makes the fact much easier to remember.
How to study capitals by region
Regional study reduces the memory burden. Learn the Baltic capitals together, then the Caucasus, Central Asia, the Caribbean and so on. Once the countries are mentally placed, the capital names attach to an existing geographic framework instead of becoming a disconnected list.
Passport progression makes recall cumulative
A correct capital answer permanently reveals that capital on the associated country passport page for logged-in players. That gives each answer a lasting result and makes it easy to see which countries still have redacted information.