Imagine if the Australian government went all-in on coal mining, to the detriment of the environment, and massively cut their science budget. It's not that hard to imagine if you follow Australian politics (which I don't suggest you do; it's painful), because that's pretty much exactly what the Australian government does.
Imagine if, say, China forged ahead with renewable energy and education. China currently has the world's largest installed capacity of hydro, solar and wind power. The number of universities in China has trebled since the turn of the century, at a rate of nearly 2 new universities per week. There are currently over 37 million university students in China. That's 150% of Australia's population.
Now apply these trajectories over 50 years. Would China still be a “developing” country? Would Australia still be number 2 in the world? Probably not.
Every country is a developing country.
Patting yourself on the back and saying you're “developed” only incites complacency. Every country has inequality, poverty, illiteracy, disease, crime, social injustices, government corruption, and corporate corruption.
We need to stop being so arrogant with our NATO and our OECD and our G20, and help each other grow and develop together, for the betterment of homo sapiens sapiens and every other species living on this planet.
As for first world, second world and third world, well, they're Cold War terms referencing allegiance to the US, Russia, or neither. They need to die a quiet death.