Okay, so imagine you have a big group of people who live in a place called Czechoslovakia. Some of these people think that their country should mainly be for people who have been living there for a long time and who are from that place, while others think that everyone should be welcome no matter where they come from. The group of people who want the country to mainly be for the people who have been there for a long time and who are from there are called the National Front.
The National Front think that it is important to protect their country and their culture, and they are worried that too many people from other places might change things too much. They want to make sure that the people who live in Czechoslovakia are the most important and that they have the most say in how things are done.
Now, some people might not agree with the National Front and think that everyone should be welcome in Czechoslovakia, no matter where they come from. They might say that everyone who lives in the country should have equal rights and be able to contribute to the society.
So, basically, the National Front is a group of people in Czechoslovakia who want the country to prioritize the people who are from there and to protect their culture, while others think that everyone should be welcomed and treated equally.