(A) Germany signed a peace treaty
(B) Great Britain formed an alliance with Belgium
(C) Russia’s monarch was overthrown
(D) ** Austria-Hungary declared war on Serbia after delivering an unworkable ultimatum
EXPLANATIONS BELOW
Concept note-1: -On July 28, 1914, one month to the day after Archduke Franz Ferdinand of Austria and his wife were killed by a Serbian nationalist in Sarajevo, Austria-Hungary declares war on Serbia, effectively beginning the First World War.
Concept note-2: -The assassination of Archduke Franz Ferdinand, heir to the Austro-Hungarian throne, and his wife Sophie in Sarajevo (the capital of the Austro-Hungarian province of Bosnia-Herzegovina) on 28 June 1914 eventually led to the outbreak of the First World War.
Concept note-3: -This assassination led to Austria-Hungary declaring war on Serbia.
Concept note-4: -When it was learned that the heir-apparent to the Austrian throne, Franz Ferdinand, was scheduled to visit Sarajevo in June of 1914, the Black Hand decided to assassinate him because of his perceived threat to Serbian independence.
Concept note-5: -According to the terms of the ultimatum delivered on July 23, the Serbian government would have to accept an Austro-Hungarian inquiry into the assassination, notwithstanding its claim that it was already conducting its own internal investigation.