Ariel Cohen: The West has a Ukraine challenge, and it's not going away

Since the Middle Ages, Kyivan Rus - the loose network of warring principalities whose borders vaguely coincide with today's Ukraine - has been exposed to waves of invaders from neighboring states. This list of aggressors includes the Normans, Mongols, Poles, Ottomans, Habsburg Austrians, Germans, and Nazis - and not least, Muscovite Russians, the Romanov Russian Empire, and Bolsheviks. Each invasion destroyed political and social institutions, produced staggering human casualties, and delayed the country's development.