I could cite dozens of times a society has gone 80 years (4-5 generations) without serious threat from foreign parties. How is our case unlike those?
The entire world has seen greater technical advances in the past 80 years than any time before, but zero percent of that is related to the politics of any one nation: either causally or effectually.
Is the last sentence satire? I can't really tell. Literally entire fields of study are dedicated to this, including one at Harvard. https://sts.hks.harvard.edu/about/whatissts.html
Also, democracy let vote for dictatorship that killed most people in human history. It's harder to implement ideologies in decentralised society.