Okay, so a really long time ago, there was a big war called World War II. Yugoslavia was a country in Europe that got involved in the war.
At first, Yugoslavia tried to stay out of the war, but then some people in the country started to disagree about what should be done. This caused a lot of problems and fighting between different groups within Yugoslavia.
Eventually, Germany and Italy came into Yugoslavia and took over the country. This made a lot of people mad, and some of them started to fight back against the Germans and Italians.
These people were called partisans, and they worked to sabotage German and Italian plans and help other people who were being oppressed by them.
The partisans were very brave and determined, and they were able to hold off the Germans and Italians for a long time. They also got help from other countries, like the Soviet Union and the United Kingdom.
Eventually, the partisans were able to push the Germans and Italians out of Yugoslavia completely. This was a really big deal because it helped the Allies (the countries that were fighting against Germany and Italy) to win the war in Europe.
But even though the war was over, Yugoslavia was still divided and had a lot of problems. It took a long time for the country to become united again and for people to start working together to build a better future.