Or be forced to not cheat and invent ways to live within our means
Because the existential threats only exist because of political malfeasance. This has never been a technological problem: even the potentially disastrous consequences of climate change only really manifest because of - again - politics. Because governments won't spend to protect their own citizens, because of corruption and greed.
Little has changed on that front in thousands of years. Technology enabled almost everything we have now - even those improvements in governance we got (i.e. mass communications and the telegraph made coordinating large empires and alleviating local resource shortages via logistics possible).
However, ever-evolving technology leads to globalisation and acceleration of processes. With shitty tech we can make lots of mistakes and pay small, local consequences. Shitty nails result in a shitty coffin. Shitty fridges result in an ozone hole. Our margin of error for doing the "politics" right is shrinking every day.
Er, not to be pissy, but isn't that a sample size of two?
I counted 18 wars with upper deaths range above 1M between 500BC and 1800AC. There were 29 of them after 1800. I didn't bother to sum the casualties. Full list:
FWIW I'm usually on the doom-and-gloom side of the argument (benefit vs. hazard of tech).
Anyway, according to the previously cited wikipedia article, the Three Kingdoms War, the deadliest ancient conflict, took toll of 40M people. but that happened over 96 years. That's 416k per year and 0.2% of global population at that time.
WW2 caused 14M deaths per year which was "just" 0.07% of global population.
Not sure how accurate these numbers are.
We are also enjoying a relatively peaceful period (despite what's happening in Syria and tens of other places) on a global scale, but history shows that every single global conflict gets more deadly. Will we survive WW3?
Let's not prise the day too early.