Alright, kiddo! Sometimes in war, countries have things called "nuclear weapons." These are really, really powerful bombs that can make a lot of damage and hurt a lot of people. The people in charge of these weapons are called "leaders."
Now, let's say that one country with nuclear weapons doesn't like another country with nuclear weapons. They might decide to threaten each other by saying, "If you attack us, we'll attack you too!"
That's where countervalue comes in. It means that if one country attacks the other, the attacked country will retaliate by destroying something of equal value to what they lost. For example, if one country destroyed a whole city with their nuclear weapons, the other country might retaliate by destroying a city of equal size or importance.
Basically, countervalue is using the threat of causing equal damage during a war to discourage the other country from attacking. Does that make sense to you, kiddo?