The Holodomor
The Holodomor was a famine in the Ukraine and Cossack territories that last through 1932 and 1933, and which killed millions of people due to starvation. Although estimates vary, it is now believed that three or four million people died of starvation, and perhaps another six million babies were not born at all or did not survive long if they were.
The Holodomor is especially noteworthy, as it was not caused by war or by natural disasters. It was caused by the Russian authorities confiscating food and supplies from the peasants, probably to quell rebellion although other scholars have argued that it was due more to economic difficulties throughout the region. Either way, it was a mass death (and some would say genocide) of the Ukrainian people.
Let us hope that such events remain only in history, and will never be repeated again.