Mission accomplished? Russia to withdraw forces from Syria on Tuesday

(CNN)Russia's bombing blitz in Syria will end today, leaving behind both significant destruction and a Syrian regime to largely fend for itself.

The first group of Russian planes left Russia's Hmeymim air base in Syria on Tuesday morning, the Russian Defense Ministry said.

The surprise announcement by Russia on Monday came as suddenly as the airstrike campaign started last September.

"The task that was assigned to the Ministry of Defense and the armed forces as a whole has achieved its goal," Russian President Vladimir Putin said.

But Russia's stated goal -- fighting terrorists like ISIS in Syria -- didn't match the reality on the ground, critics say. They point to the bombings of civilian areas as reason to believe Russia is actually helping its ally, Syrian President Bashar al-Assad, eliminate his opposition.Russia has both economic and ideological reasons to support the Syrian regime, even as many other countries blame Assad for the deaths of thousands of dissidents.

Analysts estimate Syria has spent billions of dollars on Russian-made defense equipment. And Russia doesn't believe revolutions nor regime change bring stability and democracy. It often points to the Arab Spring and the U.S.-led war in Iraq as evidence.

So it's no surprise that Russia launched hundreds of airstrikes in support of Assad over the past few months.

In a phone call between Putin and Assad on Monday, "the two leaders noted that the operations conducted by Russia's Aerospace Forces have brought about a real turnabout in the fight against the terrorists in Syria, throwing their infrastructure into disarray and causing them substantial damage," the Kremlin said.

"In this context, Mr. Putin said that Russia's Armed Forces have fulfilled their main mission in Syria."As for the Syrian President, Assad "noted the professionalism, courage and heroism of the Russian service personnel who took part in the military operations, and expressed his profound gratitude to Russia for providing such substantial help in fighting terrorism and providing humanitarian assistance to the civilian population," the Kremlin said.

But Russian forces won't leave Syria entirely. Russia will maintain an aviation support center in Syria to monitor compliance with the country's ongoing cessation of hostilities, the Kremlin said.

And Assad still has the support of two other allies: Iran and Hezbollah.

"Iran and their Shia militias, and Hezbollah, are the ground component to Russia's air involvement," Andrew Tabler of the Washington Institute for Near East Policy has said.The benefits of Russia staying in Syria no longer outweighed the costs, says James Gelvin, a history professor at the University of California, Los Angeles.

And with Russia's economy in trouble because of falling oil prices, the fight in Syria could be deemed an unnecessary cost.But the timing of Russia's withdrawal is significant for two reasons.

First, Putin's announcement came the same day Syrian peace talks resumed in Geneva, Switzerland. Members of both the Syrian regime and opposition are meeting indirectly through a mediator to try to forge a path to peace.

On the agenda: How to govern Syria, a new constitution and presidential elections.

Some see Russia's withdrawal as evidence that Putin is sending a message that Syria must reach a political solution, CNN's Moscow correspondent Matthew Chance said.

"You can't ignore the timing of this and the symbolism," he said.

German Foreign Minister Frank-Walter Steinmeier also said Assad would face new pressure.

"If a Russian troop withdrawal materializes, it would put President Assad under pressure to finally seriously negotiate a peaceful political transition in Geneva that would ensure the continuation of a Syrian state," he said.

Staffan de Mistura, U.N. special envoy to Syria, welcomed Russia's withdrawal.

He called it "a significant development, which we hope will have a positive impact on the progress of the negotiations in Geneva aimed at achieving a political solution of the Syrian conflict and a peaceful political transition in the country."

The second reason Russia's timing is significant: This week marks the fifth anniversary of the Syrian civil war.

In those five years, more than 270,000 people have been killed, half the country has been uprooted, and more than a million migrants have made the dangerous voyage to Europe, leading to an international humanitarian crisis.

The war has taken an especially brutal toll on children.