Causes of Prehistoric Mass Migrations are Uncertain

There was a big city of native people in the region that is now the St. Louis metro. Mounds and evidence are it was 50,000 people making it perhaps the largest city in the world at that time. Around the year 900 it was all gone. Theories abound. The most popular is a large drought. Now two anthropologists say there is not sound evidence there ever was a mass movement out of the area nor that there was a crippling drought. They think it was gradual and had many causes.  

The Bible's mythical story of Jews migrating out of Egypt and "out of slavery" is one of the most repeated stories of migration. It is supposed to be a historical event that led to other events in the Bible that probably most Christians believe were historical. 

Two or three decades ago, the government of Israel decided to prove the migration out of slavery and Egypt took place. It granted a big budget to a prominent professor in Israel. For many years he looked for evidence of a large migration across that desert. He noted were there is water now or where there was water back when the migration was supposed to have taken place. 

The desert is a dry place where things do not decay like in the wet tropics. Ancient artifacts have been found. None, however, have been found telling of a mass migration at the time it was supposed to have happened. The professor has admitted this on many occasions. That all Jews were slaves is also questioned. There are also records in Egypt from the period showing high level officials with Jewish names. A common theory is the story of Moses leading the Jews out of Israel and living for 49 years in the desert then defeating an enemy at Jerico are all myths made up by politicians to unite the tribes that showed up later.

We assume the first residents in the Americas were those were those we now call Native Americans. While the evidence is emerging about where they came from we don't really know why. 

As a graduate student, I dug through the library trying to find out what happened to the great tribes of Mexico, Central and South America. The ruins of huge Aztec and Inca civilizations have survived people left those areas. There was a popular theory back then, circulated by anti socialism politicians in the U.S. that the governments of Inca and Aztecs got so big and taxes so high people abandoned the societies. There is also evidence of long periods of drought. As with other theories of migrations, there well may have been many reasons.