The Pew Research Center suggests that this balance is in part due to the huge number of men that died in World War I and World War II in these regions. "In 1950, there were just 76.6 men per 100 women in the territory that is now Russia," their report reads. "That number rose steadily in subsequent decades, climbing to 88.4 by 1995 before declining again."
Moreover, the population in this region is older than the rest of the world and their older population skews more heavily female. Additionally, young men in the former Soviet Union have "an unusually high mortality rate," according to Pew.
At the other end of the spectrum, the data in many countries is skewed by policies and practices that harm women at a greater rate than men, like China's One Child Policy and similar practices in India, to name just a couple examples.