hi! you may be interested in a few previous responses to related questions

• Why does China have 1.5ish billion people but mongolia only has 2 million?

• How did the Mongol Empire transitionned from being the biggest empire ever to be a small country of 3 million inhabitants.

• How the did Mongols go for having one of the worlds largest empires to having just the developing country Mongolia is today?

• How did Mongolia go from a powerful, huge spanning empire to a third world country in the modern era?

I would also like to add that even after the internal conflicts the Mongol Empire actually split into a few nomadic tribes and those tribes eventually settled in parts like China, Central Asia, some parts of Russia and also most of the lands between Iraq and Pakistan.

As for the population the mongolians in Mongolia are not all that is left of the Mongol Empire and if we were to count every mongols descendent they would probably have more people than all of SEA.

I am not sure if this requires a source but if it is needed, the wikipedia page of the Mongol Empire shows the territory occupied by the mongols and they also show the empires that split apart. As for the population I think it is common knowledge that a HUGE bunch of people are descendent from Genghis Khan but if it were to be somehow false, feel free to tell me and I will delete that part