The nation of Syria is collapsing into a bloody, chaotic, nearly genocidal civil war. The days of the brutal regime of President Bashar al-Assad are numbered. It is not a matter of if Assad will fall, but when. The countdown is underway.

Few Americans will be sad to see Assad go. The cruel tyrant deserves to be arrested and tried for crimes against humanity, and the people of Syria desperately need to be set free. Still, few realize just how dangerous the implosion of Syria really will be.

First, in desperation, Assad could use his stockpiles of WMDs against his own people. “Syria’s Baathist dictatorship developed and stockpiled a lethal arsenal of chemical weapons including blister agents such as mustard gas and even more dangerous nerve agents (VX and Sarin),” notes Dr. Steven Bucci, a Mideast foreign policy expert with The Heritage Foundation. “These chemical munitions can be delivered by artillery, rocket launchers, Scud ballistic missiles, and aircraft. … U.S. officials believe that there are at least 50 chemical weapon production and storage facilities inside Syria.”

Washington is deeply concerned that Assad could use such weapons to defeat the rebels since conventional military means have not yet worked. “The use of chemical weapons is and would be totally unacceptable,” President Obama warned in December. “And if you make the tragic mistake of using these weapons, there will be consequences, and you will be held accountable.”

Will Assad listen? Already, some 90,000 Syrians have died in the fighting. Many of them were killed at the hands of Assad’s forces. The regime is growing desperate.

Second, Assad could choose to transfer WMD stockpiles to Iran and Hezbollah. Assad is an Alawite, not a Persian or an Arab. But over the years, Assad has built a strategic alliance with the mullahs in Tehran and Hezbollah chief Sheikh Hassan Nasrallah. Assad has long allowed Syria to be a transit country for Iranian weapons headed to Nasrallah’s forces. If he feels cornered, he might cut a deal with these allies to take his WMDs in return for an extraction from Damascus and a safe haven elsewhere, perhaps in Iran itself.

Third, Assad’s regime could collapse and WMD stockpiles could fall into the hands of radical Islamic terror organizations, including Hezbollah and/or al Qaida. Events could move too quickly for Assad. Rebel forces could gain control of the countryside and move into Damascus. This could force Assad and his senior team to flee before they get a chance to dispose of these weapons in an orderly manner.

Fourth, as Assad’s regime collapses, Syria — not just its WMDs — could fall into the hands of Iran and Hezbollah. Iranian Supreme Leader Ayatollah Khamenei and Sheikh Nasrallah are worried about Assad’s regime collapsing. But even as they are doing everything they can to prop up their ally in Damascus, they are preparing for the possibility that Assad will fall. “About one-third of Hezbollah’s troops are now in Syria,” reports Haaretz, a respected Israeli newspaper. “This reflects a strategic decision on Iran’s part not to let Syria fall into the hands of radical Sunnis, the Muslim Brotherhood, or organizations affiliated with al Qaida, even if Assad’s regime falls. Iran’s goal is to maintain its status in Syria, and hence in Lebanon as well, even after the regime falls.” This would give Iran a forward position on Israel’s borders in addition to its positions in Lebanon and Gaza.

Fifth, Syrian WMDs eventually could be used against the U.S. and/or our allies, including Israel and Jordan. What President George W. Bush feared could happen in Iraq under Saddam Hussein may happen in Syria instead. Terrorist states or groups could gain control of horrific weapons and fire them at Israel, use them against the pro-Western king of Jordan, and/or smuggle them inside the U.S. for an attack that would make 9/11 pale in comparison.

At the moment, “We have ideas as to the quantity and we have ideas as to where [Syria’s WMDs] are,” says Tom Countryman, the assistant secretary of state for international security and nonproliferation. But, he says, “We wish some of the neighbors of Syria to be on the lookout. … When you get a change of regime in Syria, it matters what are the conditions — chaotic or orderly.”

No one can predict precisely what scenario will play out. But Washington experts are deeply concerned about Syria’s future, and rightly so.

Joel C. Rosenberg, a former aide to Israeli Prime Minister Benjamin Netanyahu, is a New York Times best-selling author with nearly 3 million copies of his books in print. His latest novel is “Damascus Countdown.”

CORRECTION: An earlier version of this article incorrectly stated that Bashar al-Assad is a Sunni.