Our challenges were different from America’s. Australia is an even more intensely urban society, with close to 60 percent of our people living in large cities. Our gun lobby isn’t as powerful or well-financed as the National Rifle Association in the United States. Australia, correctly in my view, does not have a Bill of Rights, so our legislatures have more say than America’s over many issues of individual rights, and our courts have less control. Also, we have no constitutional right to bear arms. (After all, the British granted us nationhood peacefully; the United States had to fight for it.)

Because Australia is a federation of states, the national government has no control over gun ownership, sale or use, beyond controlling imports. Given our decentralized system of government, I could reduce the number of dangerous firearms only by persuading the states to enact uniform laws totally prohibiting the ownership, possession and sale of all automatic and semiautomatic weapons while the national government banned the importation of such weapons.

To make this plan work, there had to be a federally financed gun buyback scheme. Ultimately, the cost of the buyback was met by a special one-off tax imposed on all Australians. This required new legislation and was widely accepted across the political spectrum. Almost 700,000 guns were bought back and destroyed — the equivalent of 40 million guns in the United States.

City dwellers supported our plan, but there was strong resistance by some in rural Australia. Many farmers resented being told to surrender weapons they had used safely all of their lives. Penalizing decent, law-abiding citizens because of the criminal behavior of others seemed unfair. Many of them had been lifelong supporters of my coalition and felt bewildered and betrayed by these new laws. I understood their misgivings. Yet I felt there was no alternative.

The fundamental problem was the ready availability of high-powered weapons, which enabled people to convert their murderous impulses into mass killing. Certainly, shortcomings in treating mental illness and the harmful influence of violent video games and movies may have played a role. But nothing trumps easy access to a gun. It is easier to kill 10 people with a gun than with a knife.