At the end of the 19th century, a lot of trouble went into getting countries to sign agreements. The idea was that this would stop wars. But there was a problem. Each country was still suspicious of the others.
Trouble was brewing in a small place called Bosnia, which was a mix of races. Austria decided to take it over, but there were also people called Slavs, living there. Russian people are Slavs, too. As a result, Russia felt threatened.A Serbian student then shot the heir to the throne of Austria. Austria threatened Serbia, which turned to Russia for help. The war had begun.
