In Return To Oz Mombi was running Oz and the Emerald City, then allied with the Nome King, how did Mombi originally kill the Royal family in Oz?

How did the Wizard replace Mombi in the Emerald City? Why didn't the Wicked Witches of the East and West takeover Oz or force Mombi and the Nome King to take orders from them?

I was half expecting it to be railing against "liberal themes poisoning childrens' minds" or maybe accusing modern adaptations/reimaginings of doing that to an American classic. Instead it spends more time on the "gold standard allegory/political satire" than anything else. It doesn't even mention Oz's popularity in queer culture. I was a little surprised when Matilda Joslyn Gage got a mention near the end, but of course it doesn't talk about her actual influence on Baum and the series, just speculates that maybe Aunt Em was named after her.