3rd world places are just places that used to be everywhere.

When people come together into larger and larger communities, then more specialization can take place over longer periods of time.

This is if you have a stable situation, of course.

Additionally, writing and schools are critical, so knowledge can be passed down systematically. Not randomly by "tribe elders."

And the schools should be fairly open, meaning being able to be open about what they say and teach. To be able to push boundries.

Ancient Athens had writing, they had schools. They passed down architecture and philosophy in regular schools. If you are in hunter/gatherer mode, nobody really is a schoolteacher. The smartest hunter/gatherer, even if he or she was legit Einstein smart, is going to be out hunting for rabbits or deers or planting rice. You must have "extra." Extra population that supports scholars. That's why in medieval times, the Catholic Church was the keeper of scholarship. They had a lot of priest for the laypeople, but they had money to support a lot of people who hung out and did intellectual work. And, those who WERE Einstein smart joined the Catholic Church, because they figured out where they should go with their talents, just like a super smart student today knows to apply to MIT or Harvard or Princeton, etc.

Once you have the modern type university (as opposed to one or two subjects like law and religion, for example), then it all starts to snowball. Technology starts to snowball. This is one of the reasons why the Western world surpassed all others. It started in ancient Greece, and continued. England created the first modern universities at Oxford and Cambridge. Some claim it was University of Al Quaraouiyine, Morocco, but it was not a modern style university in the subject offered.

This is why England dominated the world. It passed on knowledge from generation to generation until it was absolutely the top. England's geography of being an island and cut off from mainland Europe also helped a lot.

"Third world countries", meaning hunter/gatherer, tribal, herdsman cultures, just don't have the critical mass. They simply do not have the numbers of people to make it.

The USA is the 4th most populated nation on earth. With this great population, if one out of a million is a tippy-tippy top person in some area of study, then there are going to be 330 in each area of the USA, since we have 330 million population. In every endeavor.

On the other hand, if you are in a country that has 2 million people, your odds of having that one in a million person are 3 in every area of endeavor/industry. 330 vs 3 is a big difference when you are talking about near-einstein level.

Except in a very populous country, these exceptional people will find their way to other exceptional people (usually via universities), but those in "3rd world" countries who are 1 out of a million might be stuck doing subsistence farming or shit like that. And even IF one of those 1 out of a million in Sudan, let's say, were to somehow find their way out, they would move to England or USA or Germany or France, and not stay in their poverty country. And, those countries would GLADLY give them citizenship if university was to line up behind a super skilled person.

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Culture is important. Population density is important. Inculcation of education is important (which is part of culture, I guess.). If a culture spurns education, they will never self-actualize.

People talk about islam and how they "saved" all the knowledge, and that's all great and stuff, but what have they done for us lately? The reality is that the super religious anti-education conservative elements of islam took over and fucked over the learned islamic peoples, and the conservatives of islam destroyed the smart part of islam. The same that is happening in the USA right now.

So to answer your question directly, their world countries did not "become" how they are. They are exactly like they were 10,000 or 50,000 years ago.

In order to change, you have to change. If someone is conservative and does not like change, then they will want to be like it was 100, 1,000 or 10,000 years ago. There are many, many people today who don't thing viruses or germs are a thing, for example. There are many who still believe in "gods"...like, 96% of the world believe that gods are real.

Meanwhile, the most educated do not go for that. You look at those with science degrees and only 50% believe in a god. Look at the NAS, Natural Acadamy of Science her in the USA where only top scientists are admitted, only 4% accept that a god exists.

So it's like that. Culture. Education. Knowledge. Population. Wealth. Etc.

It is a web of interconnected stuff that takes a long time to put together. England started Oxford in in 1200, and it took 800 years to make it to the peak of their Empire. Their empire fell apart because of the spread of knowledge to other parts of the world. Knowledge. Nothing else. Not war. Not WwI or WWII. Knowledge. Education.