Well, I did say that I'm no expert
My main point was that the legitimate sources of Ukrainian corruption were significantly old, closer to the end of Yanukovych's (Putin's buddy) presidency than Zelensky's. What's the saying - Nothing's older than yesterdays newspaper?
Finally, your hypothetical about Mexico is sketchy compared to the actuality of Ukraine. If you want to know how Mexico actually did respond to imperialistic invasion, study the manifest destiny era of American expansion in the 1840s and 50s. California was part of Mexico (the territory included parts of what is now Arizona and New Mexico). The Mexican government, such as it was, was corrupt, divided into factions, and just not working. Americans invaded from both land and sea. Some of the Mexicans fought the "invaders," some saw better opportunities working with the Americans. The result --- Disneyland.
A good, readable history of these events can be found in
Kearny's March by Winston Groom --- yes,
Forest Gump Winston Groom. I think he was a much better writer of narrative history than a novelist, but apparently Hollywood disagrees with me.