Realism offers a framework for understanding international relations that emphasizes the primacy of state sovereignty, the formation of strategic alliances and the balance of power as pivotal forces driving international behaviour. According to this theoretical perspective, states act primarily to secure their own interests, often through the exercise of military and economic power. Realism suggests that states will form alliances to counteract threats and to maintain equilibrium in the international system. This theoretical lens provides a compelling explanation for Russia's decisive intervention in Syria. At a moment when the Asad regime seemed on the verge of collapse, Russia's whole-scale military involvement, in September 2015, effectively altered the course of the Syrian conflict, preserving its ally and asserting its influence in the regional balance of power.

There were several factors that prompted Russia's involvement, which we discuss in this chapter, but an understanding of the deep-seated historical ties between Moscow and Damascus is required to fully appreciate what prompted Putin to save Asad.

The Soviet Union (now Russia) and Syria had developed a strong mutual alliance during the Cold War, characterized by extensive economic, military and political cooperation. The Soviet Union had been a critical supplier of arms to Syria, and the two countries had established a joint defence agreement in 1980 (Birnbaum 2016). Although relations dipped during the Gorbachev years, while the Soviet Union passed through a period of political and economic reform, they were later restored to full strength when Putin became Russian president. Therefore, when the civil war threatened to unseat Asad, Russia saw this as a strategic risk. Not only would it disrupt the established Russo-Syrian order, but it would also potentially enable Western-inclined powers to gain a foothold in Syria, thus undermining Russia's geopolitical interests in the Middle East.

In this chapter, we examine the relationship between Syria and Russia, drawing upon facets of the relationship, mentioned previously in Chapters 2 and 3, which has, to date, helped keep Syria firmly within Russia's orbit. I first evaluate the nature of the relationship (history, interests and ideology) and consider it within the context of global and regional environments. As such, the chapter accounts for Russia's enduring interest in Syria and the factors behind its decisive deployment in 2015, which changed the course of the war and saved the Syrian regime.