Mexico's drug cartels have for years armed themselves courtesy of America's love for guns.

Many Americans, wedded to their right to own guns under the second amendment of the US constitution, are viscerally opposed to stronger laws to curb weapons trafficking, out of fear that it may prove to be the thin end of a wedge that they say will result in the government confiscating all firearms.

Some are wedded to their guns out of fear of crime. Others see them as a protection against his own government, a view rooted in the American revolution and buttressed today by suspicion of Washington as the "enemy" - a constant refrain from the Tea Party movement and right wing of the Republican party. But there are many others who strongly support gun rights because of a long tradition of hunting and shooting for sport.

Today, there are estimated to be about 250m guns in the US. One in four adults own a firearm, most of them men.

That is a formidable obstacle to those who want to see greater control of guns, although they have made progress at times.

The attempted assassination of President Ronald Reagan in 1981 spawned federal controls on handguns, including criminal background checks of buyers. In 1984, Congress passed legislation banning the sale of new assault weapons.

But despite tragedies such as the shooting at Columbine high school in 1999, in which 12 students and a teacher were murdered by two fellow students, gun regulation has generally been relaxed in recent years.

The assault weapons ban expired in 2004, and Congress has declined to renew it under pressure from the gun lobby. Over the past 30 years the number of states with a law that automatically approve licences to carry concealed weapons provided an applicant clears a criminal background check has risen from eight to 38.

Central to resistance to gun regulation is one of the country's most powerful lobby groups, the National Rifle Association, which argues that existing laws should be better enforced, not new ones introduced. The group, which has more than 4 million members, describes itself as a civil rights organisation because it says it is defending constitutional rights.

The NRA has played a significant role in the election defeats of members of Congress who dare to cross it, including, in 1994, the then speaker of the House of Representatives, Tom Foley.

The association spends millions to influence presidential campaigns. While its opposition to Barack Obama did not prevent him from being elected, it did have an impact on congressional races.

The result is that the president and leading Democrats are almost silent on the issue.

"Let's be honest here: There haven't been the votes in the Congress for gun control," a Democratic party senator, Charles Schumer, said on NBC earlier this year after the issue of gun control was raised again by the wounding of congresswoman Gabrielle Giffords and killing of six others in Arizona.

Under NRA pressure, Congress is considering legislation to make it easier to carry a concealed weapon and leading resistance to a ban on the sale of weapons at gun shows without checks.

Gun rights advocates have also won important legal victories in recent years.

The supreme court in 2008 upheld a lower court ruling that struck down a ban on handguns in Washington DC. The ruling affirmed that under the second amendment of the constitution, Americans cannot be prevented from keeping a gun in their home for defence.

As hardline as the NRA may seem, there are others who are more militant.

Armed militia groups have expanded rapidly since the 1990s and two high-profile killings by federal agents – at Ruby Ridge in Idaho in 1992 when an attempt to arrest Randy Weaver resulted in the death of his wife, as she held a baby, and his 14 year-old son; and the siege of the Branch Davidian ranch near Waco, Texas the following year, which ended with the deaths of 76 people, including 20 children.

Then there was the election of President Obama.

The NRA called him the most anti-gun candidate in American history. Speculation swept the more militant gun rights advocates that Obama planned to curb gun use by taxing guns and ammunition so heavily that ordinary Americans would not be able to afford them.

Firearm sales surged in the months after his election. Gun shops in parts of the country were stripped almost bare of some weapons and ammunition.