The Sum of All Fears

During the Yom Kippur War, the Israeli Defense Force (IDF) prepares to conduct a tactical nuclear strike to stave off defeat. The necessity for the strike is averted, but an Israeli copy of a Mark 12 nuclear bomb is accidentally left on an A-4 Skyhawk attack aircraft, which is subsequently shot down over Syria. The nuclear weapon is lost, buried in the field of a Druze farmer. Eighteen years later, an Israeli police captain (coincidentally the brother of the downed pilot) shoots and kills a Palestinian activist during a peaceful public demonstration. The United States finds itself unable to diplomatically defend Israel, yet knows it cannot withdraw its support without risk of destabilizing the Middle East.
Following the advice of Deputy Director of Central Intelligence (DDCI) Jack Ryan, the U.S. enacts a plan to accelerate the peace process by converting Jerusalem into a Vatican-like independent state to be administered by a tribunal of Jewish, Muslim, and Christian religious leaders, and secured by an independent contingent of the Swiss Guards. As a nod to Israel, the U.S. Army supplies the IDF with more sophisticated equipment and agrees to construct a training base in the Negev Desert run by the U.S. Army's tank warfare specialists. To everyone's surprise, Ryan's plan seems to work. With their religious contentions appeased, the factions in the Middle East find it much easier to negotiate their disputes.