The world's youngest nation South Sudan marks four years of independence on July 9, after separating from old foe Sudan following decades of war.

A civil war in the new country broke out on December 2013 and the UN says South Sudan now ranks "lower in terms of human development than just about every other place on earth".

Here is the state of play in South Sudan after four years of freedom and 18 months of war.

WAR

Fighting began in the capital Juba when President Salva Kiir, a Dinka, accused his sacked deputy Riek Machar, a Nuer, of planning a coup. The conflict quickly spread, splitting the army and the country along ethnic lines.

It has continued ever since, with the rival leaders stoking ethnic tensions for political gain, spurning regional efforts to broker peace and ignoring threats of international sanctions.

DEATH

No official death toll has been kept. The government and rebel forces that share responsibility for the killings have no interest in tallying the deaths they might one day be held to account for, nor does the UN whose peacekeeping operation has failed to protect civilians.

In November 2014, the International Crisis Group think-tank estimated that as many as 50,000 had died and the killing has continued unabated since, while hunger and disease have added even more to the toll.

FAMINE?

Famine was narrowly averted this time last year after a massive effort by aid agencies. Now it is looming once again as fighting has forced people to flee with nothing, the planting season has been disrupted, markets have ceased trading and grain stores have been looted.

The hunger is entirely man-made, not climatic.

War-torn northern and eastern areas of the country are one step short of a famine, according to the latest assessment by the Famine Early Warning Systems Network (FEWS NET). Two-thirds of the roughly 12 million population are in need of food, medical or other aid.

DISEASE

Cholera is once again threatening to spread through the congested camps for the displaced, with 32 already dead in Juba since the outbreak was detected in June. Health services that were basic before the war are in disrepair now. Medical aid agencies, including Doctors Without Borders, have reported their facilities being targeted with life-saving operations suspended due to fighting.

THE DISPOSSESSED

More than two million people have been forced to flee during the war, leaving behind whatever meagre possessions they had to be looted or ransacked by armed forces.

Over 616,000 South Sudanese are refugees in neighbouring nations, with 480,000 of those having fled in the past year. Ethiopia hosts the majority, followed by Uganda, Sudan and Kenya.

A further 1.6 million are refugees in their own country, living in squalid displacement camps, in swamps and forests, or in villages considered safe only because they are deep inside their own ethnic fiefdoms. Over 150,000 people are sheltering inside UN bases.

WAR CRIMES?

The war has been characterised by ethnic massacres and rape. Recent attacks have included castration, rape and tying children together before slitting their throats. Others were thrown into burning houses.

Groups on all side have abducted and recruited more than 13,000 child soldiers. Around 250,000 children are facing death by starvation.

Over a dozen aid workers have been killed since war broke out, several more are missing. Fighters have shot down a UN helicopter and killed peacekeepers.

EMPTY THREATS

During peace talks held in luxury Ethiopia hotels Kiir, Machar and their entourages have run up millions of dollars in expenses while failing to sign a single lasting agreement. At least seven ceasefires have been agreed and then broken within days, if not hours.

The UN Security Council has imposed sanctions on six commanders -- three from the government side and three rebels -- who were punished with a travel ban and an assets freeze.

REGIONAL BATTLES

Over two dozen armed groups are involved in fighting characterised by shifting alliances, opportunism and historic grievances. Thousands of Ugandan troops backed by helicopter gunships are fighting for Kiir while Sudan is accused of supplying Machar's rebels with weapons. Rebels from Sudan's Darfur region have also backed Kiir's forces.

Tribal warlords like Johnson Olony are a barometer for the conflict, switching sides depending on rebel or government advances on the ground.

Trying and failing to keep the peace are 12,000 UN troops and police spread over a country about the size of Spain and Portugal combined, where even the few rough dirt roads are impassible for months at a time due to the rains.