I HAVE known Bashar al-Assad, the president of Syria, since he was a college student in London, and have spent many hours negotiating with him since he has been in office. This has often been at the request of the United States government during those many times when our ambassadors have been withdrawn from Damascus because of diplomatic disputes.

Bashar and his father, Hafez, had a policy of not speaking to anyone at the American Embassy during those periods of estrangement, but they would talk to me. I noticed that Bashar never referred to a subordinate for advice or information. His most persistent characteristic was stubbornness; it was almost psychologically impossible for him to change his mind — and certainly not when under pressure.

Before the revolution began in March 2011, Syria set a good example of harmonious relations among its many different ethnic and religious groups, including Arabs, Kurds, Greeks, Armenians and Assyrians who were Christians, Jews, Sunnis, Alawites and Shiites. The Assad family had ruled the country since 1970, and was very proud of this relative harmony among these diverse groups.

When protesters in Syria demanded long overdue reforms in the political system, President Assad saw this as an illegal revolutionary effort to overthrow his “legitimate” regime and erroneously decided to stamp it out by using unnecessary force. Because of many complex reasons, he was supported by his military forces, most Christians, Jews, Shiite Muslims, Alawites and others who feared a takeover by radical Sunni Muslims. The prospect for his overthrow was remote.

The Carter Center had been deeply involved in Syria since the early 1980s, and we shared our insights with top officials in Washington, seeking to preserve an opportunity for a political solution to the rapidly growing conflict. Despite our persistent but confidential protests, the early American position was that the first step in resolving the dispute had to be the removal of Mr. Assad from office. Those who knew him saw this as a fruitless demand, but it has been maintained for more than four years. In effect, our prerequisite for peace efforts has been an impossibility.

Kofi Annan, the former United Nations secretary general, and Lakhdar Brahimi, a former Algerian foreign minister, tried to end the conflict as special representatives of the United Nations, but abandoned the effort as fruitless because of incompatibilities among America, Russiaand other nations regarding the status of Mr. Assad during a peace process.

In May 2015, a group of global leaders known as the Elders visited Moscow, where we had detailed discussions with the American ambassador, former President Mikhail S. Gorbachev, former Prime Minister Yevgeny M. Primakov, Foreign Minister Sergey V. Lavrov and representatives of international think tanks, including the Moscow branch of the Carnegie Center.

They pointed out the longstanding partnership between Russia and the Assad regime and the great threat of the Islamic State to Russia, where an estimated 14 percent of its population are Sunni Muslims. Later, I questioned President Putin about his support for Mr. Assad, and about his two sessions that year with representatives of factions from Syria. He replied that little progress had been made, and he thought that the only real chance of ending the conflict was for the United States and Russia to be joined by Iran, Turkey and Saudi Arabia in preparing a comprehensive peace proposal. He believed that all factions in Syria, except the Islamic State, would accept almost any plan endorsed strongly by these five, with Iran and Russia supporting Mr. Assad and the other three backing the opposition. With his approval, I relayed this suggestion to Washington.

For the past three years, the Carter Center has been working with Syrians across political divides, armed opposition group leaders and diplomats from the United Nations and Europe to find a political path for ending the conflict. This effort has been based on data-driven research about the Syrian catastrophe that the center has conducted, which reveals the location of different factions and clearly shows that neither side in Syria can prevail militarily.

The recent decision by Russia to support the Assad regime with airstrikes and other military forces has intensified the fighting, raised the level of armaments and may increase the flow of refugees to neighboring countries and Europe. At the same time, it has helped to clarify the choice between a political process in which the Assad regime assumes a role and more war in which the Islamic State becomes an even greater threat to world peace. With these clear alternatives, the five nations mentioned above could formulate a unanimous proposal. Unfortunately, differences among them persist.

The involvement of Russia and Iran is essential. Mr. Assad’s only concession in four years of war was giving up chemical weapons, and he did so only under pressure from Russia and Iran. Similarly, he will not end the war by accepting concessions imposed by the West, but is likely to do so if urged by his allies.

Mr. Assad’s governing authority could then be ended in an orderly process, an acceptable government established in Syria, and a concerted effort could then be made to stamp out the threat of the Islamic State.

The needed concessions are not from the combatants in Syria, but from the proud nations that claim to want peace but refuse to cooperate with one another.

I HAVE known 

, the president of 

, since he was a college student in London, and have spent many hours negotiating with him since he has been in office. This has often been at the request of the United States government during those many times when our ambassadors have been withdrawn from Damascus because of diplomatic disputes.

Bashar and his father, Hafez, had a policy of not speaking to anyone at the American Embassy during those periods of estrangement, but they would talk to me. I noticed that Bashar never referred to a subordinate for advice or information. His most persistent characteristic was stubbornness; it was almost psychologically impossible for him to change his mind — and certainly not when under pressure.

Before the revolution began in March 2011, Syria set a good example of harmonious relations among its many different ethnic and religious groups, including Arabs, Kurds, Greeks, Armenians and Assyrians who were Christians, Jews, Sunnis, Alawites and Shiites. The Assad family had ruled the country since 1970, and was very proud of this relative harmony among these diverse groups.

When protesters in Syria demanded long overdue reforms in the political system, President Assad saw this as an illegal revolutionary effort to overthrow his “legitimate” regime and erroneously decided to stamp it out by using unnecessary force. Because of many complex reasons, he was supported by his military forces, most Christians, Jews, Shiite Muslims, Alawites and others who feared a takeover by radical Sunni Muslims. The prospect for his overthrow was remote.

The Carter Center had been deeply involved in Syria since the early 1980s, and we shared our insights with top officials in Washington, seeking to preserve an opportunity for a political solution to the rapidly growing conflict. Despite our persistent but confidential protests, the early American position was that the first step in resolving the dispute had to be the removal of Mr. Assad from office. Those who knew him saw this as a fruitless demand, but it has been maintained for more than four years. In effect, our prerequisite for peace efforts has been an impossibility.

Kofi Annan, the former United Nations secretary general, and Lakhdar Brahimi, a former Algerian foreign minister, tried to end the conflict as special representatives of the United Nations, but abandoned the effort as fruitless because of incompatibilities among America, Russiaand other nations regarding the status of Mr. Assad during a peace process.

In May 2015, a group of global leaders known as the Elders visited Moscow, where we had detailed discussions with the American ambassador, former President Mikhail S. Gorbachev, former Prime Minister Yevgeny M. Primakov, Foreign Minister Sergey V. Lavrov and representatives of international think tanks, including the Moscow branch of the Carnegie Center.

They pointed out the longstanding partnership between Russia and the Assad regime and the great threat of the Islamic State to Russia, where an estimated 14 percent of its population are Sunni Muslims. Later, I questioned President Putin about his support for Mr. Assad, and about his two sessions that year with representatives of factions from Syria. He replied that little progress had been made, and he thought that the only real chance of ending the conflict was for the United States and Russia to be joined by Iran, Turkey and Saudi Arabia in preparing a comprehensive peace proposal. He believed that all factions in Syria, except the Islamic State, would accept almost any plan endorsed strongly by these five, with Iran and Russia supporting Mr. Assad and the other three backing the opposition. With his approval, I relayed this suggestion to Washington.

For the past three years, the Carter Center has been working with Syrians across political divides, armed opposition group leaders and diplomats from the United Nations and Europe to find a political path for ending the conflict. This effort has been based on data-driven research about the Syrian catastrophe that the center has conducted, which reveals the location of different factions and clearly shows that neither side in Syria can prevail militarily.

The recent decision by Russia to support the Assad regime with airstrikes and other military forces has intensified the fighting, raised the level of armaments and may increase the flow of refugees to neighboring countries and Europe. At the same time, it has helped to clarify the choice between a political process in which the Assad regime assumes a role and more war in which the Islamic State becomes an even greater threat to world peace. With these clear alternatives, the five nations mentioned above could formulate a unanimous proposal. Unfortunately, differences among them persist.

Iran outlined a general four-point sequence several months ago, consisting of a cease-fire, formation of a unity government, constitutional reforms and elections. Working through the United Nations Security Counciland utilizing a five-nation proposal, some mechanism could be found to implement these goals.

The involvement of Russia and Iran is essential. Mr. Assad’s only concession in four years of war was giving up chemical weapons, and he did so only under pressure from Russia and Iran. Similarly, he will not end the war by accepting concessions imposed by the West, but is likely to do so if urged by his allies.

Mr. Assad’s governing authority could then be ended in an orderly process, an acceptable government established in Syria, and a concerted effort could then be made to stamp out the threat of the Islamic State.

The needed concessions are not from the combatants in Syria, but from the proud nations that claim to want peace but refuse to cooperate with one another.