Okay, so imagine you have a big group of friends who all speak different languages. Some speak English, some speak Spanish, some speak French, and some speak Ukrainian.
Now imagine that one day, someone in charge of the group decides that everyone should only speak English. They make all the French and Ukrainian speakers speak English all the time, even if it's hard for them.
This is kind of what happened in Soviet Ukraine in the 1920s and 1930s. The government in charge decided that everyone should speak Russian and follow Russian ways of doing things. They tried to make everyone stop speaking Ukrainian, even though it was their own language and very important to their culture.
But then, later on, some other people in charge realized that this was a mistake. They realized that it's okay for people to speak their own languages and be proud of their own cultures. So they stopped making everyone speak Russian all the time and allowed people to speak Ukrainian again.
It's like changing your mind about a rule that was a mistake, and realizing you should let people be themselves and respect their differences.