Why the former USSR has far fewer men than women

Why the former USSR has far fewer men than women | Pew Research Center:
"In our map above, countries depicted in the darkest blues have far fewer men than women – and the former Soviet Union stands out from the rest of the world.
This region has been predominantly female since at least World War II, when many Soviet men died in battle or left the country to fight.
In 1950, there were just 76.6 men per 100 women in the territory that is now Russia.
That number rose steadily in subsequent decades, climbing to 88.4 by 1995 before declining again.
The gender ratio in Russia is currently 86.8 men per 100 women, and the ratios in Latvia (84.8), Ukraine (86.3), Armenia (86.5), Belarus (86.8) and other former Soviet nations are similarly low.
(By contrast, the ratio in the U.S. is 98.3 men per 100 women, and the global ratio is 101.8 men per 100 women, according to 2015 United Nations data.
The U.S. has been more female than male since at least 1950, while the global population first became majority male around 1960.)
So what are the factors that set the former Soviet bloc apart?..."