For millions of people around the world, obtaining a second passport represents security, mobility and long-term opportunity. But while some countries offer relatively clear naturalisation routes, others maintain some of the strictest citizenship laws on the planet.

A passport is more than a travel document. For millions of people, it quietly shapes the opportunity of where they can work, study, invest, or even dream of going next. Some passports open doors almost everywhere. Others come with long visa queues and paperwork.