Syria: 6 simple questions for a complicated conflict

— -- As the death toll from Tuesday's chemical weapons attack on a Syrian town rises, the different sides in the six-year-old civil war have again started pointing fingers over who is responsible.

The attack -- widely blamed on the Syrian government even as Syrian President Bashar al-Assad and his international backers put the blame on Syrian rebels -- is the deadliest of its kind since Assad's government reportedly killed some 1,400 people with chlorine gas in 2013. The incident threatens to become yet another brutal milestone in a violent conflict that continues to grind on without any clear end in sight.

I thought Syria gave up its chemical weapons? But they allegedly used them in this attack?

After Assad’s chemical weapons attack in 2013, the Obama administration weighed military strikes on government targets for crossing the president’s so-called "red line." After first announcing he’d ask Congress to vote on military action, Obama’s administration then came to an agreement with Russia to peacefully remove Assad's chemical weapons.

The Organization for the Prohibition of Chemical Weapons took the lead on removal efforts, and after working on the front lines, the group announced in January 2016 that they had completed the "destruction of all chemical weapons declared by the Syrian Arab Republic."

In hindsight, the term "declared" now hangs ominously over the mission’s success.

The reality is that Syria either lied or created new stockpiles, according to Philip Coyle, a senior fellow at the Center for Arms Control and Nonproliferation.

It is unclear how many chemical weapons they still have -- or what kind. "If anything remains, we don't know what it is," said Ahmed Benchemsi, advocacy and communications director for Human Rights Watch’s Middle East and North Africa division.

Syria first obtained chemical weapons in the early 1970's from Egypt, "in response to a perceived threat from Israel," according to a 2013 Congressional Research Service report. After years of denying their existence, the government confirmed their stockpiles in 2014, saying they would only ever be used against "external aggression."

The Syrian government still maintains that they destroyed all their chemical weapons with the OPCW, blaming terror groups for Tuesday's attack.

What's the Trump administration's position? How have they responded?

President Donald Trump has condemned the attack, something he reiterated on Wednesday during a Rose Garden press conference alongside Jordan's King Abdullah.

"Their deaths was an affront to humanity," he said of the victims. "These heinous actions by the Assad regime cannot be tolerated."

"When you kill innocent children, innocent babies, little babies, with a chemical gas that is so lethal, people were shocked to hear what gas it was, that crosses many, many lines -- beyond a red line," he added later. "My attitude towards Syria and Assad has changed very much."

However, it remains unclear what that means in practice for U.S. policy, and whether the government is reconsidering military action against Assad.

While absent from Trump’s statements about the strike, his Secretary of State Rex Tillerson and U.S. Ambassador to the United Nations Nikki Haley both on Wednesday singled out Russia as a primary culprit in the attacks.

"If Russia had been fulfilling its responsibility there would not even be any chemical weapons left for the Syrian regime to use," Haley told the U.N. Security Council. "It's time the Russians really need to think carefully about their continued support of the Assad regime," Tillerson said at the State Department.

More broadly, the Trump administration -- much like its predecessor -- has primarily been focused in Syria on ISIS. It has deployed about 900 troops to provide artillery support to U.S.-backed Syrian rebels preparing to retake Raqqa, ISIS's de facto capital in the country.

Secretary Tillerson and Ambassador Haley have previously made clear that ISIS is the priority in Syria for the Trump administration. Haley has since tried to backtrack, telling ABC News' Martha Raddatz that "Assad is always a priority."

How did this conflict start?

The Syrian civil war started more than six years ago after pro-democracy protests in March 2011.

At the time, the Arab Spring was sweeping through Tunisia, Egypt and other Middle Eastern countries.

In the southern Syrian city Daraa, some teenage boys were arrested and tortured for pro-revolutionary graffiti on a school wall. Peaceful protests filled the streets, fueled by pent-up rage about limited freedoms and economic troubles.

The government quickly cracked down, killing demonstrators. But rather than quell the outrage, the bloodshed ignited it.

Soon, there were hundreds of thousands of people protesting in cities across the country. But the violence escalated, and the country was swallowed by civil war, with a rebel army of military defectors and civilians battling the government.

Since then, the fighting has attracted foreign fighters from around the world as terror groups like ISIS emerged out of the battlefield's chaos and power vacuum.

Who is fighting whom?

The civil war is defined internally by splintered rebel factions fighting both the government and each other, and externally by the participation of several regional countries and actors.

Once thought to be on the edge of collapse, the Assad government is now in control of a significant portion of the country after beating back rebels and Islamic militants. The Assad government's fortunes have been bolstered by its air force superiority and the indispensable assistance of the Russian artillery and air support.

Assad belongs to the Alawite sect of Islam, a branch that is related to Shiism, and he is also supported by the region's largest Shiite power Iran and its ally Hezbollah, the Lebanese militant group that has played an increasingly larger role in the conflict.

Meanwhile, ISIS -- the infamous and brutal terror group known the world over -- continues to hold slices of territory and operate out of Raqqa, though its de facto capital is increasingly threatened by a concerted military campaign of local and international actors.

The United States and its global coalition against ISIS have been striking at the terror group in Iraq and Syria. On its own, the U.S. has also bombed al-Qaeda-linked targets and supported and trained a diverse coalition of Kurdish, Sunni Arab and Syriac Christian fighters known as the Syrian Democratic Forces.

Complicating U.S. policy in Syria, Tahrir al-Sham (previously known as The Nusra Front and linked with al-Qaeda) continues to fight alongside the more moderate Syrian opposition, including the Free Syrian Army -- one of the original major rebel groups and a U.S. ally.

Another key force on the battlefield is Ahrar al-Sham, an umbrella group of hard-line militants that want to replace Assad with an Islamic government, but battle ISIS and at times Tahrir al-Sham as well. Many of these groups are have been secretly supported and armed by Saudi Arabia and other Arab countries.

The final key regional player is Turkey, Syria’s neighbor to the north and a fickle American ally. Turkey launched a ground campaign in northern Syria last August, sending troops, tanks and planes across the border to push back ISIS. The U.S. considers Turkey a key ally in that fight, but Turkey remains angry about American support for Kurdish groups like the YPG, which it considers a terrorist organization. In particular, the Turks are wary of rising Kurdish power and fearful of Kurdish aspirations for an independent state on Turkey's southern border.

What is the world doing?

For many Syrian watchers, human rights campaigners and international organizations, the international community has simply failed in its obligations to Syria.

That said, two major peace processes are ongoing, even if they have thus far proved unable to bring an end to the bloody conflict.

The primary diplomatic process is the long-time U.N. negotiations chaired in Geneva by U.N. mediator Staffan de Mistura, the third such envoy since the conflict began. The current version of that process was initiated last year in fits and starts, and its fifth round just concluded in March without any signs of progress.

More recently, Turkey, Russia and Iran have hosted separate peace talks in Astana, Kazakhstan. They have tried to negotiate a ceasefire, with Turkey a guarantor of the opposition's cooperation and Iran and Russia responsible for Assad's. But in the latest rounds, Syrian rebels refused to attend, and the talks ended with no agreement other than to meet again.

The Obama administration was snubbed in that process, but the Trump White House was asked to send a representative -- choosing to send its ambassador to Kazakhstan as an observer.

So what does the chemical weapons attack mean for the peace process?

A senior State Department official told ABC News, "The ball is now in Russia's court," and Secretary Tillerson communicated that to Russian Foreign Minister Sergei Lavrov when he phoned him on Wednesday. "It's the beginning of a conversation," the official said, saying it will continue next week when Tillerson travels to Moscow.

If that means renewed pressure from the U.S. that Assad must go, it could help bring Syrian rebels back to the table.

What's the endgame for Syria's conflict?

It's unclear.

With peace talks inconclusive, the power struggle continues to be fought for and decided on the battlefield -- and there's no end in sight there. Russia and Assad seem to have the upper hand for now, while the U.S. maintains its focus on the threat of ISIS, not resolving the broader conflict.

But Tuesday's chemical weapons attack could change the U.S. position, as President Trump himself alluded to.

Either way, it is hard to imagine after six years of brutal civil war that either side will come around to coexistence with the other; the opposition wants Assad out, and Assad wants to eliminate any opposition.

ABC News’s Sekar Krisnauli contributed to this report.