This video was made for entertainment purposes only. Not for historical studies or anything else. Don't take it too seriously.
Only one general is included from each country which is the one with the best military record. The displayed national flags depict the modern-day countries which represent the territory of the countries or kingdoms where the generals served in the past. Not all countries are included due to limited references.
The records may not be perfect due to possible missing data. If you encounter any errors, please let me know in the comments.