What started WW1? Who died during this cause?

The immediate cause of World War 1 that made the aforementioned times come into play was the assassination of Archduke Franz Ferdinand of Austria-Hungary. In June 1941, a Serbian-nationalist terrorist group called the Black Hand sent groups to assassinate the Archduke.

On 28 June 1914, the Austro-Hungarian heir Archduke Franz Ferdinand was assassinated in Sarajevo, leading to the July Crisis.[12][13] In response, on 23 July Austria-Hungary issued an ultimatum to Serbia. Serbia's reply failed to satisfy the Austrians, and the two moved to a war footing. 4911000 deaths in total from both sides