Syria's civil war, which has killed more than 270,000 people and forced millions to flee their homes, erupted in 2011 when government forces turned their weapons on protesters demanding political change.

The following are 10 key dates in the brutal conflict:

The many ways people have died during South Sudan's two-year civil war are well-documented, but the number killed is unknown.

Men, women and children have been shot, speared, burned, castrated, hung, drowned, run over, suffocated, starved and blown up, their corpses abandoned where they fell, bulldozed into mass graves or, in at least one case, eaten in ritual cannibalism.

Syria's war enters its sixth year next week with a glimmer of hope that a landmark ceasefire and a push for peace could help resolve a conflict that has sent hundreds of thousands fleeing to Europe.

Analysts say the past 12 months have been transformative -- with Russia's military intervention and pressure from the migrant crisis pushing world powers into renewed peace efforts.

Analysts on Thursday cast doubt on the authenticity of thousands of documents reportedly leaked from the Islamic State jihadist group, pointing out mistakes and uncharacteristic language.

The trove of documents, which includes the names, addresses, phone numbers and family contacts of IS jihadists, was handed over to Britain's Sky News by a disillusioned former member, the broadcaster said Wednesday.

As helicopters buzzed overhead, Bulgaria's Prime Minister Boyko Borisov was in defiant form at weekend exercises on the border with Greece -- meant as a show of force to any would-be migrant considering an alternative way into the EU.

"More than 400 personnel from the army, police and gendarmerie will be permanently based here," Borisov declared. "Five hundred more can be mobilized within hours."

Exactly two years after Malaysia Airlines Flight MH370 disappeared with 239 people aboard, its whereabouts remain a mystery, with only one confirmed piece of wreckage found despite the most expensive search operation in history.

Here are some of the key questions still swirling around MH370:

Hillary Clinton is on a roll. If her candidacy ever looked in doubt to an insurgent Bernie Sanders, she's all but guaranteed the Democratic nomination -- thanks overwhelmingly to African Americans.

A month after her bruising defeat in New Hampshire, where Sanders won every category of voter except those older than 65 and earning more than $200,000 a year, Clinton has chalked up massive wins.

Brazilian President Dilma Rousseff will fight for her political life in Congress, the courts and streets this week, but her path to survival is getting ever narrower, analysts say.

Rousseff faces impeachment proceedings over alleged fiscal mismanagement, while the Supreme Court is considering possible campaign funding irregularities that could end up annulling her 2014 reelection.

When Boko Haram pledged allegiance to the Islamic State group in Iraq and Syria last year, there were fears the deadly insurgency in northeast Nigeria would take on an international dimension.

The world's deadliest designated terrorist organizations -- notorious for the indiscriminate slaughter of tens of thousands of people -- were now officially linked.

Weak oil prices pose a threat to Gulf Arab states' currency pegs against the dollar, but the energy-rich region is unlikely to abandon the policy yet, analysts say.

Bahrain, Oman, Qatar, Saudi Arabia and the United Arab Emirates all keep the values of their currencies fixed against the greenback, while Kuwait has a link to a basket of currencies including the dollar.