‘Those who cannot remember the past are condemned to repeat it” …George Santayana.
History repeats itself. The reason; people repeat themselves. Particularly people who, upon reincarnating, are granted power. We remember this through ancient writings. Books preserved because they are religious. They are edited by those we are trying to remember. They take over the religions and re-write literature to their benefit. Therefore good guys are often portrayed as the bad guys and vice versa. They need to remember as well.
The Fall of Rome has been the subject of much research. Rome didn’t actually fall one day. It dissolved into a confederation of European states held together loosely by the Roman Catholic Church. As it fell Islam rose. Muslim caliphs conquered territory as far east as Indonesia and Iran. They brought with them the scholarly souls who would discover algebra and invent the telescope. Europe was in it’s dark ages during that time.
It is said the Nazis invented the atom bomb. This isn’t really true. They controlled scientists who laid the groundwork to build an atomic weapon. The war in Germany ended before they could finish their research. Some of those scientists were brought to the United States where they helped finish the work. The US then used it against Japan.
It is logical to assume if Controllers were planning to switch empires they would want to take learned souls with them. They would want to take those who they thought would be dangerous if not under their control. It is also logical to assume they would want to destroy the place they leave behind.