For more than two years, the world has stood by as the violence in Syria has intensified.
Both Bashar al-Assad's government and the opposition seem determined to fight to the death.
Arab and Western capitals have watched the events with horror, but there is little appetite for intervention: Neither the humanitarian price of well over a million registered refugees - although the real figure is much larger - nor a death toll of at least 70,000 have proved to be "tipping points" for the international community.
Nevertheless, world leaders have been drawing up contingency plans in case the situation in Syria decisively changes.
Most commentators believe that in the end, Assad's regime will collapse. Opposition forces have been regularly capturing small villages and patches of land, and the Assad regime has lost effective control of large parts of the country and many of its supply lines.
Conversations in recent weeks with ministers, ambassadors, international leaders and military commanders make clear that detailed planning is now being carried out for what comes next.
Here is what the main stakeholders in Syria are planning in the event of a major change in the conflict:
The United Nations has a project codenamed "Syria - The Day After". Secretary-General Ban Ki-Moon has put his deputy, Jan Elliason, in charge of the response. After wars in Iraq and Afghanistan, the US and its North Atlantic Treaty Organization (NATO) allies have no appetite to get directly involved in the reconstruction of Syria, meaning that by default, the UN will probably have to take the lead.
UN planners have been looking at a range of options. They fear that if Assad is eventually defeated, there could be widespread retribution against his minority Alawite sect, and the swift deployment of human rights observers and UN monitors is one possibility.
UN peacekeepers held by fighters near Syria
Humanitarian and medical supplies are being stockpiled in the region. Officials are well-aware that Syrians are dying not only as a direct result of the fighting, but due to lack of treatment for battlefield injuries and from disease.
UN officials would even consider deployment of a peacekeeping force in Syria as another option if the circumstances were right. But deploying such a force would take considerable time, and would require the authorisation of the UN Security Council, which continues to be deeply divided on all Syrian matters.
The UN has a great deal of experience working in Syria. It has had one peacekeeping operation, the UN Disengagement Observer Force (UNDOF), in the Golan Heights for almost 40 years. UN and Arab League Special Envoy Lakhdar Brahimi has one of his headquarters in Damascus. In neighbouring Lebanon, the UN has a major logistical hub, and another, larger peacekeeping force in the south of the country.
But the UN's experience in Syria in recent weeks underlines the daunting task it faces. Last month, 21 UNDOF peacekeepers were taken hostage. They were freed after negotiations, but the Japanese and Croatian contingents have already withdrawn from the mission, and much of its patrolling work is now no longer possible. And Brahimi's international staff was withdrawn from Damascus last month due to safety fears.
Many UN officials believe the next chapter in the Syrian conflict could be bloodier than this one. They will not deploy any personnel if they believe the risks are too great.
"Our humanitarian workers have already paid a price," Elliason told Al Jazeera. "We have lost … eight to nine people in our operations. It's very dangerous; to reach the most difficult areas is a risky project."
Despite growing calls on Capitol Hill for some US involvement, the Obama administration has shown no inclination towards intervention.
France and the UK are toying with the idea of sending arms to the opposition, but are currently prevented from doing so by European Union rules.
Military planners are left with the unenviable task of "second-guessing" their political masters. They know that when there is eventually an abrupt shift on the ground in Syria, events could suddenly move extremely fast, in which case they will need to have plans.
Some fear Syria could eventually split into a number of different fiefdoms, creating the possibility that the borders of surrounding countries may also be redrawn.
Securing Assad's arsenal of chemical weapons is seen as the top priority for Western powers. They fear these weapons could be used in a "last stand" by the Assad regime, or captured by armed groups. The Lebanese Shia group Hezbollah is widely thought to have operatives in Syria. A number of opposition groups, particularly those that fight under the banner of Jabhat al-Nusra, share the ideology of al-Qaeda.
It is also feared that some within Assad's military or the opposition may be ready to sell chemical munitions to the highest bidder.
In recent weeks, some US units have been involved in chemical warfare training. But Western military sources believe Assad's chemical arsenal is dispersed across numerous sites in Syria. Recovering them all would require a major military operation, involving hundreds of troops. One official told me: "The danger is that this would look like a full-scale invasion."
The US and its allies are deeply concerned about the crisis spreading. The growing humanitarian crisis could overwhelm Syria and Jordan. Last month, the number of refugees - both those registered and those awaiting registration - topped one million. As of April 1, the figure stood at more than 1.2 million.
The refugee crisis has caused worries about the stability of Syria and neighbouring countries whose borders were carved out of the Ottoman Empire at the end of World War I. Some fear Syria could eventually split into a number of different fiefdoms, creating the possibility that the borders of surrounding countries may also be redrawn.
NATO has categorically repeated over the past two years that it has no plans to intervene in Syria. However, if any of its major member nations decided to intervene, NATO may be pressured to rubber-stamp the operation.
This NATO member has more at stake than any other, and is deeply concerned about the situation across its southern border. The conflict has left Turkey with nearly 300,000 Syrian refugees, and there are thought to be many more unregistered refugees inside Turkish cities.
Ankara is also concerned about the course Syria's Kurdish minority will take, and will want to have a role in shaping the future of its neighbouring country, which is awash in weapons and increasingly hardened fighters.
Some generals in the Turkish military, which has the second-largest army in NATO, have drawn up contingency plans to take control of parts of Syria. Some reportedly have what has been described as "Ottoman ambitions".
However, there remains great distrust between the AKP, Turkey's ruling party, and the country's generals. As a result, Prime Minister Recep Tayyip Erdogan may not trust the military enough to authorise some of its more expansionist plans.
The Gulf nations, particularly Qatar and Saudi Arabia, are deeply involved in the Syrian conflict. There are no indications that they intend to put their own troops on the ground, but they will try to influence the future direction of the country with flows of money and weapons to the opposition.
Israel is deeply worried about the situation in Syria. Bashar Assad, and his father Hafez before him, publicly declared themselves to be implacable enemies of Israel. Yet the reality is that since end of the Yom Kippur War in 1973, the Syrian front has been one of Israel's quietest.
A closer relationship with Turkey is a major part of Israel's plan to protect itself from fallout in Syria.
Israel has been particularly unnerved by the collapse of stability in the Golan Heights, which it occupies. The UN force (UNDOF) is virtually confined to its base, and a number of Syrian opposition groups have been firing towards Israel. On one occasion, the Israeli military responded with a rocket strike.
The Israelis maintain that they do not want to enter Syria. But Al Jazeera has been told there are contingency plans for "containment zones" inside Syria, and, if needed, in southern Lebanon too.
Russia has been a strong ally of Syria for decades, and is believed to be providing supplies for Assad's military.
Talk to Al Jazeera: Nabil el-Araby
Russia has military personnel inside Syria at its Tartus naval base on the Mediterranean Sea. Despite a number of evacuation missions, there are still believed to be many Russian citizens living in Syria. Getting all of their citizens out in the event of a decisive change in Syria will be a key priority for Russia.
Despite the vastly divergent views on Syria held by the US and Russia, and the deadlock in the UN Security Council, there is at least one open channel of communication.
So-called "3B" meetings have taken place regularly over the last two years. The meetings are named after the three participants: UN and Arab league envoy Lakhdar Brahimi, US Deputy Secretary of State William Burns, and Russian Deputy Foreign Minister Mikhail Bogdanov. They are believed to have discussed a wide range of issues pertaining to Syria, including the securing of chemical munitions.
Iran has long been Syria's closest ally. There are always representatives of the Iranian Revolutionary Guards in Damascus, and it is safe to assume they continue to be present, providing advice.
Lebanese Shia party Hezbollah is believed to have fighters in Syria, particularly in the border areas.
If Assad falls, Iran will be concerned about loss of influence in both Lebanon and Syria. It is unlikely to take an overt military role, but instead will rely on proxy armed groups and covert action.
Iran, like Russia, knows that if Assad is toppled, or if his regime loses control in Damascus, things could change very fast. The regime has remained strong for so long because of its apparatus of control and repression, particularly in the capital. Once that crumbles, a new chapter will have begun in Syria. But many fear this new phase could be just as violent.