Okay kiddo, long long ago in India, there were two big kingdoms called Magadha and Vajji. They were both very powerful and wanted to be the boss of all the other smaller kingdoms around them. But they didn't get along very well and didn't like each other very much.
One day, the King of Magadha, named King Bimbisara, decided that he wanted to conquer the Vajji kingdom and be even more powerful. So he gathered up his army and went to fight with them.
The Vajji people were very clever and had a lot of knowledge about how to protect themselves. They had a strong government system called the "Vajjian Confederation" which meant that many smaller groups joined together to become stronger. They also had a lot of warriors who were very skilled in fighting and could easily protect their land.
So the war between Magadha and Vajji was long and tough. There were many battles fought, many people killed, and many people injured. But in the end, even though Magadha had a bigger army, the Vajjis were able to hold them off and protect their land!
The Vajji kingdom had a secret weapon that helped them win the war. This weapon was their powerful unity, and their ability to work together to defend their land. Because they were united, they were able to overcome their enemies and protect their homeland.
So that's the story of the Magadha-Vajji war. It teaches us that being united and working together can help us be very strong, even in tough times.