Russia continues to be Assad’s greatest supporter even as the Syrian conflict has killed more than 500,000 people, created more than 5 million refugees, and flattened entire cities. Here are the ways Russia enables the regime:

On the ground: Russian intervention in the Syrian civil war began on September 30, 2015, three-and-a-half years after the conflict erupted. Since that time, Russia has carried out airstrikes on targets inside Syria that it says are controlled by terrorists. It also has military advisers and special forces operating inside the country. In a puzzling statement last December, Defense Minister Sergei Shoigu said that 48,000 Russian military men had gained experience in Syria, without elaborating on what kind of experience. Russian mercenaries are also active in the country—as evidenced by the dozens who were killed in February by the U.S. military. The Kremlin denies any direct connections to the mercenaries.

Although Russian airstrikes targeted groups including ISIS and organizations that have connections to al-Qaeda, Russia also helped Assad against other, more moderate rebel groups that have fought against the regime. Prior to Russia’s intervention, a coalition of rebel groups had pushed Assad into a corner, seizing large parts of the country from the government, including Aleppo, the largest city. But with Russian help, as well as military support from Iran and Hezbollah, the Shia militia group, Assad has recaptured much of the country—and nearly all of its population centers.

Through diplomacy: If Russian military intervention assured Assad’s survival, its diplomatic support has saved him from international sanctions—if not from condemnation. Russia is a veto-wielding member of the United Nations Security Council, which means it has effectively used its veto power to suppress international action against the Syrian government. This was evident most recently on Tuesday, when Moscow stopped a U.S.-sponsored resolution to investigate the attack in Douma and determine who was responsible for the suspected use of chemical weapons there.

Russia has used its veto power concerning Syria 12 times at the UN, according to a list compiled by RTE, the Irish broadcaster. Four of those vetoes blocked resolutions that would have investigated chemical-weapons use in the country; a fifth stopped sanctions over the use of such weapons. Russia has previously also vetoed resolutions to stop the fighting in Aleppo, since violently retaken by the Syrian government; to refer Syria to the International Criminal Court for war crimes; to condemn the regime’s actions; and to sanction it for using heavy weapons in the conflict.

When the Syrian government was accused of a massive sarin gas attack that killed thousands in 2013, Russia was critical in helping save the regime from the military consequences the United States had threatened. Instead, it helped broker a deal to get Syria to declare its chemical weapons and move them out of the country. The deal did remove many tons of those substances, but Assad kept undeclared stockpiles that have been used in other attacks since.