About whether humanity can easily descend back into widespread war? Yep. Sure am. I'm also very optimistic though. We have the powerful ideal of the "Rule of Law", and some partial (incomplete) application of it even in our "UN" organization, at least to the level of rhetoric, even when the rhetoric is hypocritical. That's significant also. Even hypocritically appealing to the ideal of the "Rule of Law", even while betraying it at times, even just that appeal, is a hopeful sign that more progress is possible. Not a given. Just possible.
Civilization itself, that is the largely peaceful activities we have, like medicine, science, engineering, law, etc. -- their predominance relies actually on the proportion of the population that is trying to often do (even just often and not always), the rule Christ gave --
"So in everything, do to others as you would have them do to you."
To the extent more of humanity is trying/attempting to do what He said to do, to that extent, only, and not more, we have real hope for humanity and peace and civilization continuing without collapsing. Just to that extent, exactly.