Since the fall of 2015, Russia has launched airstrikes on opposition strongholds, deployed special forces units on the ground, and supplied Syrian government troops with food and medical aid. And this intervention has been critical to ensuring Assad's political survival.
"The regime was on the verge of collapse," said Matthew Rojansky, director of the Washington-based Kennan Institute at the Woodrow Wilson Center and an expert on U.S. relations with the states of the former Soviet Union. "Assad had lost almost everything. He was really on the ropes. Compare that to today, when he's even been emboldened enough to use chemical weapons, and it's clear the effect Russia's assistance has had in the last year and a half."
It "has really enabled the Syrian armed forces to reverse the losses they were suffering at that point," said Daniel Treisman, a professor of political science at the University of California, Los Angeles, whose work includes a focus on Russian politics and economics and comparative political economy. "Russian military involvement has succeeded in at least temporarily stabilizing the situation, allowing the Assad regime to win back territory that had been taken by the rebels."
Russia also succeeded at stymieing any U.S. or NATO intentions to impose a no-fly zone in opposition-held territory, thereby limiting the West's options for intervening had it chosen to do so, Treisman said.
Moreover, Russian President Vladimir Putin intervened in order "to draw a line in the sand against uprisings that had American and Western sympathy," said Rojansky. "He wanted to prevent that from happening in Syria."
The Kremlin's decision to defend Syria was not purely to help Assad, analysts said. The move was largely to benefit Moscow.
Syria is important to Russia for several reasons, said Andrew Parasiliti, director of the Center for Global Risk and Security at the RAND Corp. These include the country's strategic geographic location in the heart of the Middle East; Russia's naval base in the Syrian port city of Tartus, which allows access to the Mediterranean; the Hmeimim Air Base currently operated by the Russians; and the Assad regime's role in helping to counter terrorism from jihadists who could inspire Islamist extremists on Russia's doorstep in Central Asia, Parasiliti said.
"Putin thought that a victory in Damascus for forces he considers terrorists would be a huge victory for Islamist terrorists in the Middle East," said Treisman, the UCLA expert.
Also, if Assad fell, that could be perceived as "victory of the West over a traditional Russian client and Putin wanted to prevent that," Treisman said. "The intention was to preserve the credibility of the image of Russia as a reliable friend."
That friendship dates back to the days of the Soviet Union and has included military and economic cooperation, the trading of arms, people-to-people ties and cultural bonds, among other relations, experts said.
"There has been over time warmer periods and cooler periods, but that historical relationship has always been there," Treisman said.
According to analysts, cooperation between the USSR and Syria strengthened in the 1960s and1970s when the Soviets helped to develop Syria's national industries, including the oil, agriculture and transportation sectors. Soviet scientists, engineers and military instructors were among the workforce dispatched to Syria, along with weapons, machinery, and other equipment, experts said.
With the blessing of Hafez Assad, Bashar Assad's father who was then president, Moscow opened its naval base in Tartus in 1971, establishing a Soviet military foothold in the Middle East.
In 1980, Moscow and Damascus signed a treaty of friendship and cooperation, establishing specific strategic ties. The two nations fell out slightly in 1985 over disagreements related to the Palestinian cause (the Soviets backed the Palestine Liberation Organization, Syria did not) and the Iran-Iraq war (Syria supported Iran). But by the late 1980s, the friendship was back on track with Moscow continuing to provide Damascus with economic and military aid.
The early 1990s saw Syria aligning with the U.S. during the Gulf War against Iraqi dictator Saddam Hussein. And Russia's new President Boris Yeltsin, who took power in 1991, also sought to establish better relations with America. But by the end of the 1990s, Damascus and Moscow were again tighter with one another than with Washington.
A major reinforcement of the alliance between the two countries came in 2005 when Putin agreed to cancel almost 73 percent of Syria's Soviet-era debt to Russia, according to media reports. It was therefore not surprising when in 2008 Syria threw its support behind Russia's military intervention into the former Soviet republic of Georgia.
Since then, Damascus has continued to benefit from military cooperation with Russia, including the receipt of armaments, and help with infrastructure development.
In 2012, Moscow joined Beijing in vetoing a United Nations Security Council resolution calling for Assad to step down, despite the mounting death toll caused by the Syrian strongman's unencumbered killing of his own people.
Moscow has also remained adamant in its rejection of any arms embargo against Syria, arguing that it would give the Syrian opposition an unfair advantage.
Today, Syria remains one of Moscow's most significant assets in the Middle East, said Parasiliti, the RAND expert.
Autocrats in Iraq, Libya and Egypt — traditional Cold War-era allies of Russia — all have since been toppled.
"At the core was Syria," Parasiliti said. "As a long-term ally, Russia was not going to let this one go."
Author: Ann M. Simmons