Okay kiddo, so a really long time ago, there were two groups of people who lived in different parts of Europe. These two groups were called England and France. They didn't really get along very well and they kept fighting each other over different things, like land and power.
This fighting went on for a really long time and it became known as the Hundred Years' War. But after 100 years of fighting, they finally made a peace treaty and things were okay for a while.
But then, many years later, England and France started fighting again. This time it was called the Second Hundred Years' War, because it happened after the first one was over.
The Second Hundred Years' War happened because the two countries still had some disagreements and they couldn't agree on how to solve them peacefully. So they went to war again.
The war lasted for many years and it was very expensive and scary for both countries. In the end, France was able to defeat England and they signed a treaty to end the war for good.
So that's what the Second Hundred Years' War was all about - two countries fighting each other for a really long time. But it's important to remember that war is never a good thing and it's always better to find ways to solve problems peacefully.