I've always found it interesting that so many were afraid to have a female ruler in England that the whole deal with Henry 8th occurred. One documentary said it was because civil wars broke out due, but didn't give any information beyond that. What civil wars were they talking about?
I'm sorry if this question is stated wrongly for this sub. I've tried researching this on my own, but couldn't find much. Thus why I'm asking.
Your documentary was referring to the Anarchy (the civil war between Empress Matilda and King Stephen). I'll give you a bit of background, then direct you to some other great answers with a lot more detail about the Anarchy itself if you're curious.
Following the death of his only legitimate son in 1120, King Henry I had only one legitimate child left; his daughter Matilda, wife of Emperor Henry V of the Holy Roman Emperor. Following Emperor Henry's death in 1125 King Henry got his nobles to swear an oath recognizing her as his heir. He did so again in 1130.
The problem was that while he had his great magnates swear an oath to her, he didn't grant her any lands or castles on English soil so she didn't have a power base in England to enforce her claim. At the same time, following her widowhood she was married to Geoffrey of Anjou in 1128; he was unpopular amongst the English nobles and it wasn't clear what role he would have in government if Matilda was Queen. Matilda had oaths from the great magnates, and bore a son in 1133 (the future Henry II), but her position was far from secure.
When Henry I died in 1135, Matilda was far away in Anjou. She was also pregnant and unable to get to England right away. Meanwhile her cousin Stephen of Blois, count of Boulogne, found out first, raced to London, won over the people, and had himself crowned King. Matilda would return to England in 1139, and a civil war would erupt between supporters of the two monarchs that lasted until 1153 when King Stephen made a deal with Matilda's son Henry: Henry would acknowledge Stephen as King of England for the rest of his life, and Stephen would acknowledge Henry as his heir. Stephen died the next year, and Henry became King Henry II.
Source: The Struggle for Mastery: Britain 1066-1284 by David Carpenter.
For more details on the war itself and diplomatic moves, u/OnShoulderofGiants provided this great answer to a previous question.
If you're curious about King Stephen u/eonge gave this really good summary of his reign.
Here's a bit more about Empress Matilda during the war by u/toconsider.
Edited to give credit to the authors of the answers I linked.