Think of it as the downside of the Enlightenment idea that governments acquire their legitimacy solely from the support of the governed. If the people of a nation do not approve of the actions of their government, they have both the right and the responsibility to change those actions.
Or, think of it as basic ethics: no one who eats meat can be more saintly than a butcher. Everyone who benefits from citizenship in a nation gets to share responsibility for the actions of the nation.
Once the National Socialists had achieved power, in 1933, German Jews protested the actions of their government, leading to the Civil Service law and further restrictions on Jewish activities. (At this time, there were many German non-Jews who probably didn't like their government's activities but benefited a great deal from those activities.) By 1935-36, Jews in Germany had essentially no power, either to support or oppose the government. (https://en.wikipedia.org/wiki/History_of_the_Jews_in_Germany...) Thus, those who could left.
Not bloodlust, but partial responsibility. 'Tis the nature of democracy.
The people in the voting booths in the USA can no more be blamed for the USA's warmongering than the Americans who stayed home, abstaining, or people in the next country over. The US military is going to do what the US military is going to do, and to believe anything else is to be either ignorant of history or hopelessly naive.
Not voting in an authoritarian military dictatorship masquerading as a democracy is not one such instance, unfortunately.
There is no sufficient loudness of "wake up, sheeple!" that will get the US military to stop waging war (the continuation of which is entirely contrary to the will of the US people). It is an autonomous organization, unaccountable to any branch of the US government, as evidenced over and over again by the lack of resistance to it in the USG, and the lack of consequences for its members when it breaks the law.
The CIA got busted lying to Congress about hacking into Congressional computers to delete evidence of the CIA's torture program. The torture program continues, and nobody is in jail.
Certainly not like turning off a light, but it's a clear fallacy that peoples actions (or inaction) don't change policy and practice.
Put it another way, if Americans aren't responsible for the actions of America, who is? What sort of answers to that don't undermine the entire concept of the country?
If however you are a functioning member of a society and do things to support it you are partially to blame for the things that society does. That amount of blame is not the same for everyone - and for some people it is so minimal it hardly warrants mentioning - but you do have a share.
on edit: as an example we can say with some surety that the one white man in 1800s American that should not be charged with culpability for slavery would be John Brown (although he probably would not feel the same way) - there are undoubtedly others but we can point with some justification at John Brown and say that guy pretty much not to blame for any of that shit.
I'm certainly not recommending that people have to do these things either, just to being clear eyed about things - you can't benefit from your society's actions and then say you don't share any blame from what it does without some extreme dropping out of the system.
I mean, I can see where you're coming from. But at this point we are really at the fringes of culpability and it's more of an issue of semantics and definitions.
so yes, each of those 1.3 billion probably have an atom of culpability, so minimal it hardly warrants mentioning.
I'm a citizen of Denmark, I have some share of culpability in the wrongs my country does - I do a little to minimize those wrongs (when I see them) by voting against the perpetrators but that's about it - I support the country and it is partly my fault because I am too comfortable to do what would be required to completely absolve myself of any culpability because hey, I'm pretty okay (as most people throughout history have said)
Collective punishment refers to the punishment communities en masse for the actions of individuals, that may be being harbored by some members of that community.
Just because something is done in a collective manner does not absolve the members of that collective from the outcome.
Bernie Sanders is an American who was advocating against the Iraq War. He was clearly not culpable for it, and his causal role was to lower the probability that it would go ahead. This is an example of why it would then be wrong to blame "Americans" as a collective for the Iraq War. Bernie Sanders, a member of that collective, deserves either zero blame or negative blame (if that even exists).
To extend your example: Bernie Sanders as a citizen, and further a politician, acquires an amount of the collective responsibility for the countries actions in the Iraq War. Bernie Sanders as an activist has more than discharged that responsibility by actively countering it.
A citizen who has done nothing to mitigate or counter the actions is left only with the share of collective responsibility; however large or small that may be, it's real.
Are they expected to single-handedly (or collectively) organize and engage in a bloody civil war, thereby gaining culpability for that? Blaming people for the actions of their nation / elected officials is absurd. All a person can do is vote for the best candidate in front of them and vote at face value.
Representative democracy takes power away from people. If it were a direct democracy, then yes, I'd say sure, people bear responsibility. But it's not. It's a system designed to be manipulative and serve wealthy and powerful interests, and the only way to change it is either very, very slow, or very, very bloody.
Governments != people of a nation people often / usually don't approve of governmental actions.