Burgfriedenspolitik is a very big word that means something important happened in the olden days. During a time called World War I, people from different countries fought against each other. The fighting was very bad, and many people got hurt or died.
But then something happened that was different. The leaders of the countries fighting decided to work together so that they could win the war. They made an agreement to stop arguing and fighting with each other so they could focus on the war. This agreement was called burgfriedenspolitik.
It was like when you are playing a game with your friends and you stop arguing so you can focus on winning the game together. That's what they did, but on a very big and important scale! They stopped their arguments and worked together to fight the war, so that they could win and then start living in peace again.