One cause of the outbreak of world war I was caused by? The outbreak of Russian revolution? Rising tensions among European powers? The killing of a Serbian national? Or the invasion by Germany of Belgium?

Answer 1

The killing of a Serbian national, Archduke Franz Ferdinand, was the immediate cause of the outbreak of World War I. His assassination in Sarajevo in 1914 set off a chain of events that led to rising tensions among European powers and ultimately culminated in the declaration of war.