For the Russians, the agreement keeps their client, President Bashar al-Assad, in power, cements their military foothold in Syria and increases the Kremlin’s influence in the Middle East. American intelligence officials told the Obama administration this year that Russia’s goal was to help Syrian forces retake Aleppo so that Russia could pursue a political settlement on stronger terms. This month, the rebel stronghold in eastern Aleppo fell to pro-government troops backed by Russian air power.

For Mr. Assad’s government, the cease-fire is an implicit acknowledgment that it lacks the military might to take back all of Syria. The agreement fails to address what role, if any, Mr. Assad will play in Syria’s future. Russia has not addressed the issue and is now less likely to press Mr. Assad to step down after the military victory in Aleppo, analysts said.

For Turkey, the cease-fire reflects a changed strategy. A longtime backer of the Syrian opposition, the Turks have in recent months backed away from their demand that Mr. Assad step down and instead have shifted their focus to limiting Kurdish autonomy in northeastern Syria. Turkey has also taken in more Syrian refugees than any other country, causing a crisis that could wane if the cease-fire holds.

“This is a window of opportunity that has been opened and should not be squandered,” President Recep Tayyip Erdogan said, referring to the cease-fire, at a news conference in Ankara, Turkey’s capital.

While the Obama administration was not included in the cease-fire discussions, the Russian foreign minister, Sergey V. Lavrov, said that President-elect Donald J. Trump could join the process after taking office next month. Mr. Trump never objected to Moscow’s growing influence in the Middle East throughout his campaign and promoted the possibility of greater cooperation with the Russians in fighting the Islamic State.