I've already explained why I omitted the civil war. WW2 presented an existential threat to the K, prior to that, the country had experienced multiple partial or complete takeovers by foreign powers every few centuries, going back to the Romans.

I didn't say anything about 'crushing optimism.' Good vibes only is a contemporary American idiom that essentially says 'don't bother me with any negative opinions.' This can be a mild desire to socialize with chilled out people, or breezy way of indicating you don't give a shit about other people.