In The Crown (TV series), Queen Mary says that three great monarchies were brought down by "their failure to separate personal indulgences from duty." What were they that brought their downfall?

by Ty-the-Squirtle

https://www.youtube.com/watch?v=FnBjb5imPLY

Here's the entire scene that portrays it. In the scene, the letter states that she has "seen three great monarchies brought down through their failure to separate personal indulgences from duty." It's speculated to be the Russian, Austrian, and German monarchies that were ultimately brought down by World War 1. While I don't know if the letter was real or not, the major question is what was the failure to separate personal indulgence from duty that ultimately brought the downfall of the (speculated) German, Austrian, and Russian monarchies?

Also if I'm allowed to ask minor questions:

  • What were the "three great monarchies" that Queen Mary says in the letter? I think it was likely referring to the Russian, Austrian, and German monarchies, but I'd like to make sure!

  • Was that letter real?

prewars

I'd like to ask if anyone has any good sources for the history of the British royal family, or even the more prominent ones in Europe, with a focus on personal lives/relationships. It's always been interesting to me but Wikipedia is pretty lacking, obviously.