The assassination of Archduke Franz Ferdinand, heir to the Austro-Hungarian throne, on 28 June 1914 set off a crisis that led to a war. The killing was the spark that ignited the world and began a series of events that resulted in the death of millions of people, until the outbreak of World War II two decades later.

The war was caused by a number of factors, including imperialism, nationalism, and competition for power and influence. The leaders of the major powers decided to go to war because they believed it was necessary for them to defend their countries or expand their power and territory.

Imperialism: The countries of Europe had been experimenting with imperialism, which was a way to build up their country and become more powerful. This led to tension and rivalry between countries, since each country wanted to be the biggest.

Nationalism: The nations of Europe were influenced by their cultures, which made them choose loyalties based on their ethnic background rather than shared interests or ideals. This caused many people to be angry, and they started to fight against each other.

Germany and Austria-Hungary went to war with Russia, France, and Belgium to protect their countries from the other three. This led to a war that killed millions of people and made Europe weak.

After the war, the world was still divided and warring between two superpowers, Russia and Germany. This lead to many unresolved political problems, including the creation of the United Nations. The world was dominated by these two rival superpowers for the next half-century.