1 There are almost a billion guns in the world

Eight years ago it was estimated there were at least 875m guns in the world. Today, if you include antique and homemade guns, that number is probably greater, fed by gun and ammunition industries across more than 100 countries. Police forces worldwide are said to have about 26m firearms. Armies are thought to hold about 200m. Civilians, though, claim the rest and are by far the biggest owners of guns. About 12bn bullets are produced every year, almost enough to kill every person on the planet – twice.

2 Over a million people a year are shot

Estimates suggest there are about 600,000 violent deaths annually – 340,000 of these are thought to be at the end of a gun. If you take into account that, at a bare minimum, for each person shot and killed, three will survive, about 1,360,000 people are shot by someone else every year.

Such global figures mask regional horrors. In Puerto Rico, for instance, about 95% of homicides are committed with a firearm. Brazil, with more than 35,000 gun homicides a year, has the most firearm deaths in the world. And San Pedro Sula, in Honduras, has the burden of being known as the most violent city in the world outside a war zone, with a murder rate of 173 per 100,000. This weekend’s gun battle between rival biker gangs in Waco, Texas, underlines the fact that in certain areas of the US, gang homicide rates are over 100 times the murder rate among the wider population. Without a doubt, the right to bear arms fuels this extremely high level of violence. To put these figures in perspective, the England and Wales homicide rate is less than one per 100,000, with only 5% of those killed by guns.

The majority of those shot are men. Globally, male homicide rates are almost four times that of women. Women account for the majority of domestic violence gun killings, but in some places, the gender disparity in terms of overall armed violence is stark. The World Health Organisation reported in 2014 male homicide rates at about 11 times greater than female rates in Brazil, 14 times in Honduras and 18 times in Venezuela. In Venezuela, 90% of those killings were with a gun.

3 Guns influence suicide rates

The WHO estimates that more than 800,000 people kill themselves each year, and one commonly used way is with a firearm. There are no concrete figures on how many people shoot themselves globally, but we know the prevalence of guns in a society affects how people choose to take their lives. So in England and Wales, with its tight gun laws, only 2% of suicides are gun deaths. In the US, with almost as many guns as there are people, gun suicides account for the majority of all suicides – more than 20,000 a year. Indeed, there were 92 American children under the age of 14 who shot themselves in 2011.

Guns play a role in this. In 2006, the Israeli Defence Force witnessed a disturbing number of suicides in its ranks. In an effort to reduce this number, the IDF banned soldiers from taking rifles home on the weekends. Suicides fell by 40%. An army review later concluded: “Decreasing access to firearms significantly decreases rates of suicide among adolescents.”

4 The US constitutional right to bear arms has deep consequences

The US has more guns per person than any other country in the world. Stemming from a constitutional right to bear arms, it has given birth to an industry that in 2013 helped sustain a quarter of a million jobs, directly or indirectly, creating $38bn in annual economic activity.

Today, at almost 140,000, there are about 10 times more federally licensed sellers in the US than there are McDonald’s. They have plenty to sell – more than 10.8m guns were manufactured in the US in 2013, a 220% rise from a decade before. This does not include the 5.5m guns imported into the US that year.

Where there are more guns, there are more gun deaths. The US has the highest per capita rate of firearm murders of all developed countries. While figures are hard to come by, data from the Center for Disease Control shows that in 2013 there were as many as 100,598 non-fatal intentional shootings in the US (the lowest estimate was 23,842). That year saw 33,636 fatal shootings (including suicides).

The data offers stark reading. In 2013, FBI figures show 1,075 people under the age of 19 killed by guns in the US, 37 of them under five years old. More American teenagers and children were killed that year by gunfire than US military in any given year in Iraq or Afghanistan.

Army revolver from the American civil war ... as guns have evolved, so too have medical responses to the injuries they cause. Photograph: Bob Pool/Getty Images

5 The gun has been behind some of the great advances in medical history

As guns have evolved through the centuries, so too have medical responses to the injuries sustained from them. In the 14th century, gunpowder’s harm caused doctors to believe bullets were contaminants. This led to the practice of burning the wound to rid the body of poison. By the American war of independence (1775-83) surgeons were suggesting that, if a gunshot wound was to be sewn up, a piece of onion was best put inside, and the wound reopened after one or two days.

By the Crimean war of the 1850s, though, Florence Nightingale’s efforts to clean hospitals had a notable impact on patient mortality, which dropped from 52% to 20%. Joseph Lister’s experiments applying carbolic acid to wounds also helped reduce death rates. And Roentgen’s development of the X-ray in 1895 helped pinpoint fabric, bullets and bone fragments. The impact of these discoveries was revolutionary: research into the Spanish-American war in 1898 suggests that 85% of US casualties survived.

Medical innovations in gunshot trauma continues today. Tranexamic acid, used to ease heavy menstrual flow, has also helped save the lives of haemorrhaging gunshot patients. Syringes containing tiny sponges can stem a gunshot wound in seconds.

6 Iceland bucks the trend when it comes to gun violence

We’ve seen that where there are more guns, there are more gun deaths; Iceland, however, is different. About 1% of the Icelandic population belongs to a gun club, and an estimated 90,000 guns exist in this land of about a third of a million people, putting it about 15th in the world ranking of guns per capita. But whereas in 2012, 47,136 people were murdered in Brazil and 14,827 people were estimated killed in the US, only one person died violently in Iceland.

So rare an event is murder that when, in 2013, a 59-year-old man was shot dead by Icelandic police, the incident was a major scandal, mainly because it was the first time the country’s police force had shot and killed anybody, ever. The fact that the police generally do not carry guns, a small population, strict gun registration laws, a close-knit community spirit, and a liberal punitive legal system partly explain why Iceland’s unusual relationship with guns.

An armed policeman at the scene of the Waco shootout. Photograph: Jerry Larson/AP

7 Handguns are by far the biggest killer

Much is made about the bloody impact of assault rifles and high-powered guns. Mother Jones reported that between 1982 and 2012 over half of the 62 US mass shooters examined killed using guns with high-capacity magazines, assault weapons, or both. The reality, though, is that pistols and revolvers are used in the vast majority of gun killings. In São Paulo, one report found 97% of firearm murder weapons were handguns. FBI data from 2012 shows over 90% of gun murders in the US where the firearm was identified were with handguns. We might well focus on semi-automatic rifles being used in shootings, but it’s the handgun we should really be worried about.

8 Guns do not make women safer

Many studies have concluded that having a gun in the marital home puts women at greater risk than men. In the US, women are estimated to be 11 times more likely to be murdered with a gun than women in any other developed country. Perhaps this is not that surprising when you take into account that only nine states in the US prevent people jailed for stalking from buying a gun, once they are released. In 2014, it was estimated that almost 12,000 convicted stalkers in the US were still permitted to carry a gun under federal law. American gun control pressure groups, like Everytown, also claim the presence of a gun makes it five times “more likely that domestic violence will turn into murder”.

Despite this, gun lobbyists push the line that a gun makes a woman safer. Wayne LaPierre, the executive vice-president of the National Rifle Association, has said that “the one thing a violent rapist deserves is a good woman with a gun”. And gunmaker Glock’s Wrong Girl advert, where a young woman foils a would-be attacker, explicitly extols that fact. This despite the fact that, as a comprehensive American scientific review concluded: “There is compelling evidence that a gun in the home is a risk factor for intimidation and for killing women in their homes.”

9 Guns from the US fuel violence far afield

In July 2014, a US government report found 43% of the serial numbers of 474,823 weapons given to the Afghan national army by the US Department of Defense could not be accounted for or had been duplicated. In Iraq, the Pentagon lost track of about 190,000 rifles and pistols given to the Iraqi security forces. And this year, US officials claimed the Pentagon was unable to account for more than $500m in military aid to Yemen.

What happened to all of these guns is unknown. But ammunition magazines “identical to those given to Afghan government forces by the US” have been found on dead Taliban fighters, and US-made firearms have been captured from Islamic State forces in Iraq and Syria.

It is not just the likes of Isis that has been armed with American guns. About 253,000 US guns are estimated to cross into Mexico annually. The US government also found that 76% of firearms traced in Costa Rica and 61% in Belize in 2013 were either manufactured in or imported into the US.

This wave of guns has had consequences. There were 120,000 homicides estimated to have taken place in Mexico between 2007 and 2012 – mainly with American guns. About 70% of traced guns there were found to have come from the US. And in the four years following the lifting of semi-automatic firearm restrictions in the US there have been an estimated 2,500 additional homicides in Mexico. Such are the international consequences of America’s love for the gun.

10 The US is the only country that relaxes gun laws after a massacre

When 13 people were murdered in Aramoana, New Zealand, lifetime gun licences were replaced by 10-year ones. The massacre of 16 in Erfurt, Germany in 2002 led to the psychological screening of buyers under the age of 25. And in Australia in 1996, the Port Arthur massacre paved the way for a general ban of semi-automatic weapons and a nationwide gun buyback scheme.

Such is the trend globally: a mass shooting leads to a public debate about the need for tighter gun controls and politicians respond.

The US, though, is the only country in the world where, following a mass shooting, the nation has responded with loosening, not tightening, gun laws. After 23 people were killed in a mass shooting in Texas in 1991, the state pushed through a law permitting the carrying of concealed weapons. Even the murder of 26 children and adults at Sandy Hook Elementary School in December 2012 saw a call for fewer, not more gun law restrictions. It was reported a year later by PBS that 27 American states had passed 93 laws expanding gun rights, including measures that let people carry concealed weapons in churches and campuses, or even to use them in self-defence when drunk. Some schools even now allow their teachers to go armed.

Has this made the US safer? Many say not. In the 18 months before Sandy Hook, there were 17 gun deaths in US schools. In 18 months following Sandy Hook, 41 deaths were reported.

An Oklahoma company even came up with a solution. They sell bullet-resistant blankets to protect schoolchildren – a pad that they claim protects against 90% of all weapons used in school shootings.

• Iain Overton is the director of policy and investigations at the Action on Armed Violence charity.

• His book Gun Baby Gun: a bloody journey into the world of the gun, is published by Canongate, price £18.99. To order a copy for £15.19, go to bookshop.theguardian.com or call the Guardian Bookshop on 0330 333 6846. Free UK p&p over £10, online orders only. Phone orders minimum p&p of £1.99.