What unprecedented ultimatum did Austria make to Serbia, which many historians believe contributed to the start of WWI?

A. Requesting permission for Austrian officials to continue their investigation into the assassination of Archduke Ferdinand on Serbian territory
B. Demanding access for Austrian military troops along the Belgium border in an attempt to head off the impending French army
C. Asking the German government to support the Serbian military, which was much smaller than Austria's, in an attempt to make the coming battle more fair
D. Suggesting that the Serbian government pay an incredibly large amount of money to the Austrian government to guarantee that Austrian troops would not advance inside the Serbian borders

Austria presented Serbia with a list of ten ultimatums demanding an investigation into the assassination of Archduke Ferdinand on Serbian territory, leading to Austria-Hungary declaring war on Serbia, which contributed to the outbreak of WWI.

Explanation:

The unprecedented ultimatum that Austria made to Serbia, which many historians believe contributed to the start of WWI, was a list of ten ultimatums demanding a full-scale investigation into the assassination of Archduke Ferdinand by Austrian agents on Serbian territory.

Germany supported Austria-Hungary by promising unconditional military backing if any other nation joined the conflict, leading to Austria-Hungary declaring war on Serbia on July 28, 1914.

The ultimatum escalated tensions in Europe, setting off a chain of events that resulted in World War I.

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