All it takes is just one event to represent both the spark and the fuel for such a massive and destructive global conflict. The event that involved the assassination of Arch Duke Francis Ferdinand led to a long line of conflict among the countries in Europe. Since most countries are interconnected, whether through resentment or alliances, a situation in one country could lead to a chain of retaliation throughout a continent.
Archduke Francis Ferdinand was an Austro-Hungarian who went to Sarajevo on June 28, 1914. Though Austria-Hungary ruled a number of Slavs, Slavs were not given equal rights. The lack of equality led to the resentment of Slavs towards their Austro-Hungarian rulers and eventually their need for independence or in other words, nationalism. When it was revealed that Ferdinand was planning a visit to Sarajevo on the same day Serbia "was conquered by the Turks at the battle of Almsfelde in 1398", many Serbians became outraged.
They felt it was on insult and therefore 7 Serbians from the nationalist group known as the Black Hand devised a plan to assassinate Ferdinand.
Ferdinand and his pregnant wife, Sofie escaped the first attempt of assassination but the second time around, they were not as fortunate. Princip, a 19-year-old Serbian boy shot both Ferdinand and Sophie. This event eventually led to Austria-Hungary's demands that Serbia refused to fully follow. With this, Austria-Hungary went to war with Serbia. Being that Russia supported Serbia, Russia went to war against Austria-Hungary as well. Austria Hungary's allies, that included Britain and France, then became involved. Eventually, many other countries in Europe became involved, no matter how much they did not want to. Due to the formation of alliances, two countries' feud became every other countries' problem.
Since many counties are interconnected, especially with the formation of alliances,