An autocratic country could easily spread propaganda in the democratic country, because of “free speech” rules that most democratic countries have, but a democratic country cannot easily spread its propaganda in the autocratic country.
An autocratic country can buy an election in the democratic country, but the democratic country cannot easily coup an autocratic country.
Are all democracies are doomed to fail?
Is the future of humanity, autocracy? For the rest of humanity’s existence?
Autocracies are short-lived power grabs by certain people or groups of people. They pillage what they can, oppress who they want, and then run or fall when the walls start closing in.
Many have come and gone during our history on this planet. Many more will rise and fall.
See Plato’s five regimes.