MOSCOW — On one jasmine-shaded block in the Syrian port city of Latakia, Natalya lives three doors away from Nina, two from Olga, across a narrow alley from Tatyana, and a short walk from Yelena, Faina and Nadezhda. They are all women from the former Soviet Union who married Syrian men. Pan out to the greater expanse of Syria and the number of Russian wives grows to 20,000, the human legacy of a cold war alliance that, starting in the 1960s, mingled its young elites in Soviet dormitories and classrooms.

This unusual diaspora offers some insight into the many-stranded relationship between the two countries, one that makes the Kremlin reluctant to cast off Syria’s president, Bashar al-Assad. Russia has strategic interests in Syria, including arms contracts that amount to $700 million a year, and a tiny port on the Mediterranean Sea that is its last military base outside the former Soviet Union.

But there is also a human factor, set in motion 50 years ago when social ties were forged among young people who met in college. Walk into any government ministry or corporate headquarters in Syria and you will almost certainly find men who spent their 20s in Russia; many brought home wives and raised children in Russian-speaking households....