In a country where tens of thousands die every year from gun violence, fueling a never-ending debate over firearms, the U.S. Supreme Court will hear a case on Monday that could expand the rights of gun owners, setting the stage for a further loosening of gun legislation nationwide.

Where can I take my gun?

It all started with a much smaller case in 2013. Under New York City law, gun owners could hold firearms at home and transport them to a limited number of shooting ranges and hunting areas within the state.

Without a "carry" license however, they were not allowed to take them to other locations, or out of the state. 

The New York State Rifle & Pistol Association – the local affiliate of the powerful U.S. gun lobby, the National Rifle Association (NRA) – filed a lawsuit with three plaintiffs, arguing that they should be allowed to carry their firearms to a secondary home, or shooting ranges and competitions outside New York.

To prevent them from doing so violated their Second Amendment rights – the clause in the U.S. constitution that protects people's right "to keep and bear arms" – they said.

Read more: The NRA: Shaping U.S. gun legislation amid mass shootings

The U.S. District Court for the Southern District of New York dismissed the claims in 2015, a decision affirmed by a federal appeals court in 2018.

The plaintiffs remained undeterred however and decided to take the case further to the Supreme Court.

Commentators have already dubbed "New York State Rifle & Pistol Association v. City of New York" the biggest guns case to appear before the Court in a decade.

A conservative court

More than just a local issue, the case could pave the way for crucial changes to gun legislation nationwide, pro-gun activists hope.

The Supreme Court has rarely ruled on Second Amendment issues in the past. In 2008, it stated for the first time that individual gun rights are protected by the constitution.

But what has gun control advocates especially worried is the Court's newly conservative slant, since Brett Kavanaugh was sworn in last year to replace retired Justice Anthony Kennedy.

Whereas Kennedy was considered a swing vote among the nine justices, siding alternately with his conservative and liberal colleagues, Kavanaugh is seen as a staunch conservative who backs an expansion of gun rights.

In a 2011 dissenting opinion while he was still a U.S. Court of Appeals judge, he argued that a ban on semi-automatic weapons and a requirement to register them in the District of Columbia were "unconstitutional."

"The courts must enforce… constitutional rights even when they have 'controversial public safety implications'," he insisted. 

His presence on the Court now gives conservatives a five-member majority.

And if the Supreme Court rules in favor of the New York plaintiffs, this may be used to challenge other existing gun laws – from background checks and registration requirements to assault weapons bans – gun control advocates fear.

"The future of life-saving gun safety laws across our country is very directly on the line with this case," said Hannah Shearer, litigation director of the Giffords Law Center to Prevent Gun Violence.

A question of 'mootness'

Bizarrely, the Supreme Court will be hearing an issue that, technically, has already been solved.

In June, New York City announced it was easing its restrictions on where gun owners could take their firearms, following a push by gun control advocates, who hoped this might prevent the New York State Rifle & Pistol case from reaching the Supreme Court.

The move sparked a heated debate between both sides over whether the issue was now "moot" and should be dropped from the Court's agenda.

"There is no longer a case or controversy because the changes in state and municipal law give petitioners all they seek," the respondents argued. 

The Office of Solicitor General, representing the U.S. government, finally ruled on November 15 that "in the United States' view, respondents have not established that this case is moot" and the hearings could go ahead. 

It added however that the parties should "be prepared to discuss mootness at oral argument."

A ruling is not expected before June or July 2020.

Guns galore

The U.S. remains the country in the world with the most civilian-held firearms, with 120.5 for every 100 residents, far ahead of countries like Yemen, Serbia, Iraq or Pakistan, according to the 2018 Small Arms Survey.

Frequent mass shootings in public places and schools however have made gun legislation a hot topic, with-well entrenched sides battling it out in the courts, in Congress and in the media. 

While the Trump administration is widely seen as being close to the gun lobby, a Pew Research Center poll in early October found 60 percent of Americans wanted stricter gun legislation. In a Fox News survey in August, 90 percent said they favored background checks, while 67 percent backed a ban on assault weapons.