In America, basketball is the poor man’s sport - urban poor people play it more than any other sport. To make it the world’s most popular sport, urbanize the shit out of the world. Have most people live in cities that have paved areas where basketball can work. Once you have a flat, paved surface, all you need is two hoops (which are rather durable in weather, and shit, if it comes to it, you can use a single hoop in a pinch) and a ball. In an urban setting, it isn’t that much more complicated than soccer (or any other football - makes me wonder why rugby isn’t among the top five sports in the world when it doesn’t take terribly much to play it.)
So in short, basketball as number one would take:
1. Lots of urbanization (getting there)
2. Soccer to get scandalized (we’re talking about FIFA here so it’s definitely possible)
3. Individual stars to take on the world a la Ronaldo and Messi (picture LeBron James and Steph Curry being household names in China, South Africa, Italy and Brazil to a similar extent of soccer stars.)
A FIBA World Cup and a lot more competition for the gold medal in basketball (as in it’s not USA vs the field every four years) would help as well.