(A) French attacks on German colonies
(B) The U.S. entering the war because of Russia
(C) The Serbians assassinated Archduke Ferdinand
(D) ** Germany invaded Belgium on the way to France
EXPLANATIONS BELOW
Concept note-1: -Germany declared war on Russia in support of Austria and on France because of her alliance with Russia. Britain declared war on Germany in support of Belgium and France, and on Turkey because of her alliance with Germany.
Concept note-2: -On September 3, 1939, in response to Hitler’s invasion of Poland, Britain and France, both allies of the overrun nation declare war on Germany.
Concept note-3: -The official explanation focused on protecting Belgium as a neutral country; the main reason, however, was to prevent a French defeat that would have left Germany in control of Western Europe.
Concept note-4: -On 4 August the British government sent an ultimatum to Germany and declared war on Germany at midnight on 4–5 August Central European time. Belgium severed diplomatic relations with Germany and Germany declared war on Belgium.
Concept note-5: -Germany realized that a war with Russia meant a war with France, and so its war plans called for an immediate attack on France – through Belgium – hoping for a quick victory before the slow-moving Russians could become a factor.