Did you write down notes as you studied for your documentary videos, or did you just write the script as you researched the history?
i wrote down notes. for history of the world it was very intense. days and days of notes, gathering info from different times and places. until i thought i had ... "everything" [slams head into wall because it's clearly not everything but i've been on 500-1000AD for litterally a week, note taking only] and then just jump around until i can find some clever way to say all of that in 1 sentence and have it still be true, exciting, and directly relevant to whatever was said before