The U.S. backed the country in its independence struggle. Now, it is needed again.
A U.S. intelligence agent is assisting with the prosecution of suspects accused of killing a South Sudanese aid worker and raping his foreign colleagues.
Soldiers killed 114 civilians, raped countless women and attacked funerals in a recent offensive, according to a U.N. report.
Almost half the population face food shortages and 100,000 people are at risk of immediate starvation in South Sudan.
The rest of the 4,000-strong contingent is expected in the country later this year.
At least 82 aid workers have been killed since 2013 in South Sudan, the U.N. says.
Nearly half the population will not have a reliable food source by summer.
The U.N. has warned of possible genocide in South Sudan.
The Security Council has failed to impose an arms embargo on the conflict-hit state.
A U.N. human rights commission said that ethnic cleansing was already underway in South Sudan.
Russia said U.N. mission in South Sudan is "in ruins" after damning inquiry on peacekeepers.
Kenyan head of the U.N. mission in South Sudan was sacked Monday.
South Sudan's crisis is getting worse, and international bodies are standing idly by.
European and Middle Eastern firms use African middlemen to sell arms to the war-torn state.
Report accused top officials, including Salva Kiir and Riek Machar, of benefiting from the conflict.
Top South Sudanese officials have accrued fortunes during the country's civil war.
Machar fled South Sudan after fighting in the capital Juba in July.
The deposed vice-president fled South Sudan earlier in August.