A protester looks on as clouds of smoke and crowd-control agents rise shortly after the deadline for a city-wide curfew passed in Baltimore, Maryland. Credit:Reuters The book, Solutions: America's Leaders Speak out on Criminal Justice, was launched at the Brennan Centre for Justice at the prestigious New York University's law school. Its foreword is written by former president Bill Clinton and it contains essays by Hillary Clinton, other leading Democrats like Vice-President Joe Biden, and Cory Booker, an African-American senator from New Jersey who is considered a future leader. But it also included many of the leading Republican presidential contenders such as Rand Paul, Marco Rubio, Scott Walker and Mike Huckabee. Even firebrands like Ted Cruz and Rick Perry contributed. Though he did not contribute, the leading Republican presidential candidate, Jeb Bush, has also dramatically softened the zero-tolerance stance of his years as governor of Florida. One of the book's co-editors, Nicole Fortier , said she was surprised at the reception she was given when she contacted these candidates and asked for a contribution.

Mexico's most-wanted drug lord Servando "La Tuta" Gomez is escorted by police officers during a media conference about his arrest in Mexico City in February. Credit:Reuters Rather than hesitating, the various leaders jumped at the chance to contribute. Their offices wanted feedback and advice. Some asked if they could have more length. Art Bilek, left, of the Chicago Crime Commission, announces in 2013 that Joaquin "El Chapo'' Guzman, the head of Mexico's Sinaloa Cartel, has been named Chicago's Public Enemy No. 1. Credit:AP But it was the content of the submissions that stunned her when they began arriving.

Each politician from across the viciously divided American political spectrum agreed that mass incarceration must end. People take part in a march commemorating four months of the disappearance of 43 students from Ayotzinapa, at the Zocalo square in Mexico City. Credit:AFP This turnaround in political will is extraordinary. The war on drugs began under President Richard Nixon, but it was Bill Clinton who opened a new front in 1994 after another surge in crime statistics across America. Demonstrators sing reggae songs and dance at the intersection of North and Pennsylvania Avenues in Baltimore. Credit:Reuters

That year he introduced an omnibus crime bill that expanded the death penalty and encouraged states to lengthen prison terms and adopt mandatory sentences. It scrapped funding for inmate education. As a result of these laws, and other tough measures adopted by federal and state governments, America now has the biggest per capita prison population in the world. A young boy greets police officers in riot gear during a march in Baltimore after the decision to charge six officers, including one with murder. Credit:Reuters The figures are dizzying. It locks up one in 100 American adults and has 25 per cent of the world's prison population with just 5 per cent of the world's population. One in 28 children have a parent in prison. Considered together America's prison population would be the size of its 37th largest state. Half of all offenders are in prison for non-violent offences.

Leading Republican presidential candidate, Jeb Bush, has dramatically softened the zero-tolerance stance of his years as governor of Florida. Credit:AP The Clinton crime bill was, the Atlantic magazine recently noted, backed by every Congressional Democrat but one. In the new book Clinton concedes, "plainly, our nation has too many people in prison and for too long – we have overshot the mark". Texas Republican Ted Cruz says the inmate population in the federal Bureau of Prisons rose by more than 400 per cent since the late 1980s. Credit:AP It is the growing consensus that by incarcerating vast swaths of the urban poor America has broken families, shattered whole communities, increasing the chances of further incarceration.

In inner cities where crime is highest and police are most needed, police are seen as occupying forces rather than civil servants. They are feared and loathed by the populations that need them most. President Barack Obama wants to reform criminal justice laws, which will mean overturning some measures introduced by former president Bill Clinton. Credit:Reuters While America's unemployment rate is rapidly falling, its long-term unemployment remains stubbornly high, in part because employers are reluctant to hire ex-cons. This in turn promotes recidivism. A new campaign to reverse that perverse result has been launched. Called ban the box it calls on employers to pledge not to ask applicants to tick a box if they have a record. Instead, it asks them to ask the question in an interview when the applicant might have a chance to explain their situation. Senator Rand Paul notes judges have condemned the effect of mandatory minimum sentences. Credit:AP

What has driven this remarkable change in political will is debatable. The protests on streets in many American cities, now commonly referred to by activists as "uprisings" might have contributed to the urgency of the movement. It is also clear that during the long recession states could no longer afford to keep locking people up, especially when a single inmate cost them as much as a police officer or teacher might each year. Social scientists are now identifying so-called "million-dollar blocks" – those in poor neighbourhoods with collapsing infrastructure, the government is spending $US1 million ($1.3 million) each year locking up residents of single blocks. A Columbia University lab identified many such blocks and found that when inmates returned home they could expect to last an average of three years before they would again be jailed.

But the overwhelming factor – the factor that makes this an issue that politicians are willing to address – is that there has been an unprecedented collapse in the crime rate. Since the era when Clinton went tough on crime and New York City adopted its infamous "broken windows" zero-tolerance policy, American crime rates have fallen by half. One of the more interesting observers of crime and punishment – and policing in particular – in America is Radley Balko, who noted in a recent Washington Post column that people vote on criminal justice issues only when they are in fear, and Americans no longer fear crime as they once did. "While most people continue to erroneously tell pollsters that crime is getting worse nationwide, on the more pertinent question – whether Americans fear walking alone in their own neighbourhood – the percentage answering yes hasn't been above 40 per cent since the early 1990s." This is because, Balko argues, "in 2013, there were nearly 9000 fewer homicides, about 27,000 fewer rapes, and about 368,000 fewer aggravated assaults than there were in 1991, even though the country's population increased by 64 million people."

Asked if a de-escalation in the war on drugs might see crime levels rise, the Brennan Centre's Nicole Fortier says no. In the book What Caused the Crime Decline? the Brennan Centre found incarceration had a limited and diminishing impact on crime levels, one that had almost become irrelevant by 2000, accounting for just 1 per cent of the decrease. The true cause is layered and complicated, the book argues, and includes increasing incomes and consumer confidence, decreased alcohol consumption, and the better targeting of police resources through the use of statistical analysis of crime patterns. Another study by the National Academies' National Research Council found that "the growth in incarceration rates reduced crime, but the magnitude of the crime reduction remains highly uncertain and the evidence suggests it was unlikely to have been large". With the panic over crime receding some states have already begun ending the drug war, the crucial contributor to mass incarceration. Many states have decriminalised possession of small amounts of marijuana, while two – Colorado and Washington, as well as the city of Washington, DC, – have taken the extraordinary step of legalising the drug for recreational use.

President Barack Obama, who has made criminal justice reform central to his final years in office, has ordered his Justice Department not to intervene by enforcing federal drug laws. This turnaround in America's war on drugs is already having an impact on law and order around the world. Prohibition enforced by strict criminal sanctions was largely an American invention imposed around the world through treaties and diplomatic pressure. On Thursday the United Nations held a debate at its New York headquarters on the issue at the request of Uruguay, Mexico and Colombia, which argued that as some American states no longer criminalises all drug possession, they should no longer be compelled to wage the American drug war. They want the treaties rewritten.

The meeting was greeted by a letter from a group of 100 drug policy and human rights organisations, including the American Civil Liberties Union and Human Rights Watch, calling on the UN to reform the way it treats drugs and for member countries to respect those governments that have or will legalise or decriminalise narcotics. "Existing US and global drug control policies that heavily emphasise criminalisation of drug use, possession, production and distribution are inconsistent with international human rights standards and have contributed to serious human rights violations," they write. "Criminalisation of the drug trade has dramatically enhanced the profitability of illicit drug markets, fuelling the operations of groups that commit abuses, corrupt authorities, and undermine democracy and the rule of law in many parts of the world." The groups believe "human rights principles, which lie at the core of the United Nations charter, should take priority over provisions of the drug conventions". Some at the UN already acknowledge the problem. In 2012 the Office of the High Commissioner for Human Rights issued a report finding that "excessively punitive approaches to drug control have resulted in countless human rights violations, including the right to health".

The discussions in New York on Thursday were in preparation for the UN General Assembly Special Session (UNGASS) on Drugs in 2016. The special session was originally scheduled for 2019, but was brought forward due to pressure from Latin American countries, where governments have become increasingly concerned about how the war on drugs has affected crime and development in the region. They believe, as many American policymakers now do, that imprisonment is far more harmful to drug users – and to their communities – than the drugs they are being imprisoned for using. Whatever happens in the UN next year it now seems certain that whoever wins the 2016 presidential election will continue with efforts to reduce America's prison population, rein back zero-tolerance policies and de-escalate the war on drugs. Though the political leaders who contributed to the Brennan Centre book do not have a common approach on how to achieve this, there are areas of broad agreement, Fortier says. Most agree on the need to steer the mentally ill and non-violent offenders away from prison and that mandatory minimum sentences are destructive and need to be repealed. Whatever the outcome it will take years to unpick the diabolical confusion of law and regulation that today can still force American judges to steal whole lifetimes from the pettiest offenders.

Back in Baltimore on Thursday the Baltimore Sun told the story of Ronald Hammond, who appeared in a local courtroom in 2011 on a charge of possessing 5.9 grams of marijuana. The district court judge thought the case was preposterous. "5.9 grams won't roll you a decent joint," Judge Askew Gatewood said. "Why would I want to spend taxpayer's money putting his little raggedy butt in jail – feeding him, clothing him, cable TV, internet, prayer, medical expense, clothing – on $5 worth of weed?" Gatewood urged Hammond to plead guilty so he could free him on parole. But then it turned out that Hammond was already on parole for selling $40 worth of crack to an undercover officer. With a parole infraction Hammond copped a mandatory minimum sentence of 20 years. He is now due for release in 2028, though the current maximum penalty for possession of 10 grams or less is a $100 fine.

He told the Sun that when he heard the sentence, "A chill went from the top of my head to the bottom of my toes." The US has 5 per cent of the world population, but 25 per cent of its prison population.

Almost one in 100 American adults are in prison.

The US prison population grew by 700 per cent from 1970 to 2005.

in 15 black males aged 18 years or older is incarcerated.

Forty per cent of the prison population is African-American, but only 12 per cent of the general population.

One in 28 children has a parent in prison.

At the current pace, one in three African-American men will spend some time in prison.

Nearly half of state prisoners are locked up for non-violent offences.

The US spends $US260 billion ($330 billion) on criminal justice every year.

Over the last four decades, the US has spent more than $1 trillion on its drug war. CHANGE OF HEART "A very small number of people commit a large percentage of serious crimes – and society gains when that relatively small group is behind bars. But some are in prison who shouldn't be, others are in for too long, and without a plan to educate, train, and reintegrate them into our communities, we all suffer." – Former president Bill Clinton "If the United States brought our correctional expenditures back in line with where they were several decades ago, we'd save an estimated $28 billion a year. And I believe we would not be less safe. You can pay a lot of police officers and nurses and others with $28 billion to help us deal with the pipeline issues." – Former senator and secretary of state Hillary Clinton (Democrat)

"​You may assume mass incarceration exists because people are committing more crimes. But that is not true. Violent crime has plunged in recent decades; the rate has declined roughly by half since 1993. In fact, numerous studies have shown that incarceration rates cannot be tied to crime rates." – Senator Cory Booker (Democrat, New Jersey)​ "According to a 2012 Government Accountability Oﬃce report, the inmate population in the federal Bureau of Prisons increased by more than 400 per cent since the late 1980s because of lengthening sentences." – Senator Ted Cruz (Republican, Texas) "An Arkansas prison oﬃcial once told me that 88 per cent of incarcerated inmates at his prison were there because of a drug or alcohol problem or because they committed a crime in order to get drunk or high. As he astutely observed, we do not have a crime problem, we have a drug and alcohol problem." – Former governor Mike Huckabee (Republican, Arizona) "A chorus of judges has lamented the eﬀect of mandatory minimum sentences as 'unjust, cruel, and even irrational'.One judge declared, '[F]airness has departed from the system as a result of these laws."​ – Senator Rand Paul (Republican, Kentucky)​ Centre'sSolutions: American Leaders Speak out on Criminal Justice