A lot of the talking points you're repeating here are intentionally misleading, although I recognize that you may not intend to mislead — you may merely have been misled yourself. If that is the case, you should probably re-evaluate your criteria for judging the credibility of information sources. As you will see, although it seems unlikely to you that almost all gun violence is international warfare, it is in fact true.

I know it can be difficult to read a "wall of text" like this, but accurately conveying the reality of a nuanced situation cannot be done with perky infographics and bullet points, particularly when it is necessary to carefully dissect the half-truths propagated by dishonest parties. I estimate that reading this will take you about four minutes; it's 1632 words. I hope you have the attention span.

As you may not know, most of those 45'222 "gun-related injury" deaths are suicides; as the BBC article you linked explains, only 19'384 were actually gun violence, up from under 15'000 the year before. (The US had 20'982 homicides overall in 2020, but some were not by gun.) Typically suicides by gun are about twice as common as homicides by gun in the US, but apparently 2020 was an exceptionally violent year there.

Unsurprisingly, suicides by gun are enormously more common among people who live in a home with a gun, which accounts for most of the positive correlation between gun death and gun ownership.

Moreover, there is strong evidence that access to a gun increases people's risk of suicide — it's not merely that people blow their heads off because it's easier than hanging yourself or overdosing on drugs, they actually killed themselves when they would have stayed alive if they hadn't had a gun. This effect is, at best, very weak with homicides, to the point that we don't know whether either population gun prevalence or gun ownership is a weak risk factor or a weak protective factor for homicide.

70 million people died in World War II, which is 3500 years' worth of those 19'384 people per year. If we divide those 70 million over the last century, World War II alone accounts for 700'000 deaths per year, seven times the number you cite of 100'000 per year.

5.4 million people died in the Second Congo War (1998–2008), 270 years' worth of those 19'384 people per exceptionally violent year, but to be fair most of them were held at gunpoint in refugee camps where they died of disease or starved to death, rather than being directly shot; only 350'000 were actually direct violent deaths, which is only a bit more than twice as many as were killed in the US during the same period. (But Congo's population is one third as big.) You will note that 5.4 million people killed over 11 years is 490'000 deaths per year, several times the 100'000 wartime deaths per year you cite, and that's just one war of several that were going on at the time, though it was the biggest one.

The US Civil War involved something like 700'000 deaths, which is about 30–40 years of 2020-level US peacetime gun violence, though, again, out of a much smaller population.

You've inaccurately paraphrased Chelsea Bailey's claim in the NBC article (https://archive.fo/TlCkV); she's talking only about the 1.2 million members of the US armed forces killed in US wars, entirely omitting the people who lived in the countries the US was invading. She even omitted the American civilians killed in the US Civil War! The Vietnam War alone, for example, killed at least 1.3 million people, probably closer to 3 million. The 2020 US's 19'384 gun murders per year would take 150 years to reach that number. Bailey counts the Vietnam War as 0.09 million; she didn't even deign to count Vietnamese and Laotian people as the Constitutional three-fifths of a person. Of course, she also included about a million gun suicides in her 1.53 million gun deaths in the US since 1968. For some reason, the source she cited for this number (a number I think is roughly correct, if misleading when presented as an indicator of gun violence) was an MMWR article from 1994 which documents about 700'000 gun deaths, including suicides, since 1968. Evidently her intended audience isn't the kind of person who checks citations.

It should be unsurprising that when one country invades another, the country that gets invaded suffers the bulk of the deaths. On this count, the US is exceptional, both in not having been invaded since 1865 or arguably 1815, and in invading other countries at a truly unprecedented rate, one that is as far as I know unexcelled even by the Soviet Union, the British Empire, and Genghis Khan. This is known to be an important factor in its relatively high peacetime murder rate.

It is indeed very inaccurate to say that most gun violence occurs in the US, even excluding international warfare; countries with higher homicide counts include Mexico, India, Brazil, and Nigeria, and almost all homicides in Mexico, Brazil, and Nigeria are with guns, just like the US. (India has a much lower murder rate than the US, but because its population is five times as large, it has about twice as many murders, though very few are with guns.)

I'm not sure why comparison articles like the BBC article omit Mexico, Brazil, and Nigeria; it's possible that, like Chelsea Bailey at NBC, they don't consider human deaths important if the people who die aren't white, though Bailey went even further by implicitly dehumanizing US civilian and white European victims of warfare as well. Alternatively, instead of attempting to portray the reality of the world accurately, as I am doing here, they are cherry-picking data points in order to justify a preconceived conclusion.

I don't have current worldwide death statistics handy, unfortunately, but the WHO's burden-of-disease report from 2004 says that in 2002, within the category of "intentional injuries", 557'900 people died of "violence" (i.e., murder), 872'662 of "self-inflicted injuries" (suicide), and 171'021 of "war", which is 1.7 times the 100'000 per year figure you cite for wartime deaths. The US had 15'700 homicides that year, according to that report, 2.8% of world homicides. You will note that this means that 97.2% of homicides, and a somewhat lower fraction of gun homicides, were outside the US. So saying that most gun violence occurs in the US is very inaccurate indeed.

Some subset of those 557'900 were killed with guns in peacetime; it would take 125 years of that death rate, even if it were all guns, to equal the 70 million killed in only World War II, out of, again, a much smaller world population. But of course in the 77 years since World War II there have been many other wars, some of which I've mentioned above. 2002 just happened to be a year without much war.

In conclusion, almost all gun violence is international warfare. Statistically the picture is very clear; though the intensity of warfare varies by orders of magnitude from one year to the next, the average number of war deaths is about an order of magnitude higher than the average number of peacetime gun murders. (Also, as you said, most peacetime gun murders are by family members or intimate partners, not robbers or gangs.)

There do remain three possible quibbles.

First, possibly we should count the Great Leap Forward, the Cultural Revolution, the Holocaust, the Cambodian Killing Fields, and so on, as "gun violence", and they were not for the most part international warfare. Most of the people killed in the Great Leap Forward were starved to death rather than being shot, and most of the people killed in the Holocaust were gassed, but in both cases gun violence was the foundation of the mass murder system, just as with the Second Congolese Civil War. These deaths (Rummel coined the term "democides" as a generalization of "genocides") account for a surprisingly large fraction of 20th-century violent deaths, comparable in fact to warfare. The US prison system does not rise to the level of these atrocities, as its direct death toll is actually fairly low, but you could argue in the same way that the millions of people every year in the US who are arrested by police with guns and then held in prisons with gun-armed guards are also being subjected to gun violence, even if it doesn't kill them.

Second, possibly World War II was some sort of freak accident that will never be repeated, and the ensuing 60 years of Pax Americana are really more typical of what to expect from now on. Given that Vladimir Putin threatened to start a second nuclear war this week, I am skeptical of that thesis, but it might turn out to be correct. Even in that case, though, peacetime gun homicide has a smaller death toll than warfare; it just stops being an insignificantly small fraction of the total.

Third, as you say, maybe when a missile blows up a hospital and kills half the people inside, or a bomber covers a screaming family with napalm, we shouldn't count that as "gun deaths" because no actual guns are involved, so maybe we should derate the war deaths by some fraction to account for that. We don't really know what fraction of war deaths are from gunshots, especially in cases like Congo with many irregulars and deliberately inaccurate official casualty reports, but even in cases like Vietnam, where there's over a factor of 2 uncertainty in the total death toll. But it seems implausible that gun deaths in war are an order of magnitude less than total deaths in war, so this is not a big enough effect for peacetime gun murders to exceed wartime gun violence.