The United Nations has declared a famine in parts of South Sudan, the first to be announced anywhere in the world in six years. There have also been warnings of famine in north-east Nigeria, Somalia and Yemen. Why are there still famines and what can be done about it?
What is happening in South Sudan?
UN agencies say 100,000 people are facing starvation in South Sudan and a further 1 million there are classified as being on the brink of famine. This is the most acute of the present food emergencies. It is also the most widespread nationally. Overall, says the UN, 4.9 million people - or 40% of South Sudan’s population - are "in need of urgent food, agriculture and nutrition assistance".
"Many families have exhausted every means they have to survive," says the UN’s Food and Agriculture Organization representative in South Sudan, Serge Tissot.
The basic cause of the famine is conflict. The country has now been at war since 2013 and more than 3 million people have been forced to flee their homes.
As World Food Programme country director Joyce Luma says: "This famine is man-made."
"The people are predominantly farmers and war has disrupted agriculture. They’ve lost their livestock, even their farming tools. For months there has been a total reliance on whatever plants they can find and fish they can catch," says Mr Tissot.
Crop production has been severely curtailed by the conflict, even in previously stable and fertile areas, as a long-running dispute among political leaders has escalated into a violent competition for power and resources among different ethnic groups.
As crop production has fallen and livestock have died, so inflation has soared (by up to 800% year-on-year, says the UN) causing massive price rises for basic foodstuffs.
This economic collapse would not have happened without war.
What does the declaration of famine mean?
The UN considers famine a technical term, to be used sparingly. The formal famine declaration in South Sudan means people there have already started dying of hunger.
More specifically, famine can be declared only when certain measures of mortality, malnutrition and hunger are met. These are:
At least 20% of households in an area face extreme food shortages with a limited ability to cope;
Acute malnutrition rates exceed 30%; and the death rate exceeds two persons per day per 10,000 persons.
Other factors that may be considered include large-scale displacement, widespread destitution, disease outbreaks and social collapse.
The declaration of a famine carries no binding obligations on the UN or anyone else, but does bring global attention to the problem.
Previous famines include southern Somalia in 2011, southern Sudan in 2008, Gode in the Somali region of Ethiopia in 2000, North Korea (1996), Somalia (1991-1992) and Ethiopia in 1984-1985.
The possibility of three further famine declarations in Nigeria, Somali and Yemen would be an unprecedented situation in modern times.
"We have never seen that before and with all of these crises, they are protracted situations and they require significant financing," World Food programme director of emergencies Denise Brown told the Guardian. "The international community has got to find a way of stepping up to manage this situation until political solutions are found."
What can be done in South Sudan?
In the immediate term, two things would be necessary to halt and reverse the famine: More humanitarian assistance and unimpeded access for humanitarian agencies to those worst affected.
UN agencies speak of handing out millions of emergency livelihood kits, intended to help people fish or grow vegetables. There has also been a programme to vaccinate sheep and goats in an attempt to stem further livestock losses.
But, says Ms Luma, "we have also warned that there is only so much that humanitarian assistance can achieve in the absence of meaningful peace and security".
The areas where a famine has been declared are in parts of Unity State seen as sympathetic to the rebels.
Some UN officials have suggested President Salva Kiir’s government has been blocking food aid to certain areas. There have also been reports of humanitarian convoys and warehouses coming under attack or being looted, either by government or rebel forces.
Although it denies the charges, President Kiir has now promised "that all humanitarian and development organisations have unimpeded access to needy populations across the country".
But apart from that, there has been no indication that the huge suffering of civilians will prompt South Sudan’s warring parties to stop fighting.
Why are there food security crises elsewhere?
The common theme is conflict.
Yemen, north-east Nigeria and Somalia are all places where fighting has severely disrupted stability and normal life.
In Yemen, a multi-party civil conflict has drawn in regional powers, causing widespread destruction, economic damage and loss of life.
Nigeria and Somalia have faced insurgencies by extremist Islamist groups Boko Haram and al-Shabab, respectively, leading to large-scale displacement of people, disruption of agriculture and the collapse of normal trading and market activities.
In some cases, conflict has compounded pre-existing problems.
Yemen has long-standing water shortages and successive governments have been criticised for not doing more to conserve resources and improve the country’s ability to feed itself. (Even before the conflict started, nearly 90% of Yemen’s food had to be imported, Oxfam says.)
In other cases, shorter term climatic factors may be relevant.
South Sudan and Somalia have both been affected by a months-long drought across east Africa.
How is it different for more stable countries?
In Kenya, the government has declared a national disaster because of the drought and announced a compensation scheme for those who have lost livestock.
The Kenya Red Cross has been making cash payments, distributing food vouchers and aid and helping livestock owners sell off weakening animals before they die.
This kind of ameliorative action is much less possible or likely in countries riven by war.
UN assistant secretary general Justin Forsyth told the BBC: "Nobody should be dying of starvation in 2017. There is enough food in the world, we have enough capability in terms of the humanitarian community.
"In South Sudan, [the UN children’s agency] Unicef has 620 feeding centres for severely malnourished children, so the places where children are dying are places we can’t get to, or get to only occasionally. If there was access, we could save all of these children’s lives."
The US-based Africa Center for Strategic Studies says 19 African countries are facing crisis, emergency, or catastrophic levels of food insecurity.
Of these, 10 are experiencing civil conflict. Eight of these are autocracies and the source of 82% of the 18.5 million Africans who are internally displaced or refugees, the ACSS says.