BEIJING (NYTIMES) - China on Monday (May 31) increased the number of children married couples are legally permitted to have - to three from two - in an effort to stave off a looming crisis as the birthrate in the world's most populous country steadily falls.

The country of 1.4 billion people, which introduced a one-child policy in 1980 to slow population growth, has implemented some of the world's most invasive family-planning practices. But as the country's workforce has aged, the government has increased the legal size of families.

Here is a look at China's population policy over the decades.

1978

With the failed Communist Party policies of the Cultural Revolution and Great Leap Forward behind it, China looks for ways to slow the growth of the world's most populous nation, which is nearing 1 billion people.

The central government approves a proposal in which family-planning offices encourage couples to have one child, at most two. Some areas go further and begin to enforce a "one-child" rule.

1979

A national conference of family-planning officials pushes forward proposals that couples be restricted to having one child, and the state news media promote the idea.

Chinese provinces experiment with measures to curb population growth, including providing additional food rations for couples in Sichuan province pledging to have only one child.

1980

The Communist Party orders its 38 million members to have only one child, one of a series of measures that are gradually expanded and aimed at curbing population growth to zero by the year 2000.

The policy begins to be enforced nationwide, with some exceptions made for ethnic minorities and rural families.

1982

The National People's Congress endorses a new constitution that for the first time enshrines birth control as every Chinese citizen's duty.

2003

In Guangxi province, where family-planning regulations are strictly enforced, parents trying for sons sell their baby girls on the black market. At the time, 80 per cent of trafficked babies were girls, according to a Chinese academic.

2008

Chinese officials say they will begin studying how to move away from the country's one-child restriction, but they caution that any changes would come gradually and would not mean an elimination of family-planning policies.

Although enforcement of the policy has softened in many places, there are still reports of forced sterilisations and abortions.

2014

The Chinese government eases the one-child policy, permitting couples nationwide to have two children if one of the spouses is an only child.

2015

China ends the one-child policy, announcing that all married couples will be allowed to have two children, in a bid to reverse the rapid ageing of the labour force.

2020

Chinese academics warn the country's leaders that decades-long family-planning initiatives have led to a precipitous decline in population growth, setting the stage for potential demographic, economic and even political crises in the near future.

The decline in the birthrate and an increase in life expectancy mean there will soon be too few workers to support an enormous and ageing population, the researchers warn.

2021

The Politburo, the Communist Party's top decision-making body, announces that it will allow all Chinese couples to have three children, ending the two-child policy that failed to increase the country's declining birthrate.

The news comes weeks after census data shows there were just 12 million births the previous year, the lowest number since 1961.

The new policy will "help improve our country's population structure and help implement a national strategy to actively respond to the ageing population", the government says.