ELI5: Explain Like I'm 5

Population exchange between Poland and Soviet Belarus

Okay, so imagine you and your friend both have a bunch of toys, but you want some of your friend's toys and they want some of yours. You agree to trade some toys with each other so you both have different toys to play with.

Now, let's say Poland and Soviet Belarus were like you and your friend, but instead of toys they had people living in their countries. Some of the people in Poland wanted to live in Soviet Belarus, and some of the people in Soviet Belarus wanted to live in Poland.

So, in order to make everyone happy, the two countries decided to exchange some of their people. People from Poland who wanted to live in Soviet Belarus were allowed to move there, and people from Soviet Belarus who wanted to live in Poland were allowed to move there too. This was called a population exchange.

It wasn't just a small group of people who moved, though. It was a very big group of people – in fact, over a million people moved from one country to the other! This happened in the years after World War II, when borders and countries were changing a lot in Europe.

Overall, the population exchange was a way for people who wanted to live in a different place to do so, and for countries to try to make their populations happier.