Complex sentence: In the First All-Union Census of the Soviet Union (1926) the registration of people as Little Russians was restricted, and people in the Ukrainian SSR had to choose between the Ukrainian and Russian nationality or even were automatically registered as Ukrainians.
Split into simpler sentences: In the First All-Union Census of the Soviet Union (1926) the registration of people as Little Russians was not allowed. People in the Ukrainian SSR had to choose between the Ukrainian and Russian nationality or even were automatically registered as Ukrainians.