After Austria-Hungary declared war on Serbia, the conflict escalated as various countries honored their alliances and obligations. Here’s how other countries became involved:
a) Russia's Role: Russia, as an ally of Serbia, stepped in to defend the Serbs against Austria-Hungary's aggression. When Austria-Hungary declared war on Serbia, Russia mobilized its army in support of Serbia, viewing the conflict as a matter of Slavic solidarity and national interest.
b) Germany's Role: Germany, allied with Austria-Hungary, declared war on Russia in response to Russia's mobilization. Germany viewed Russia's actions as a threat to its interests and felt obligated to support its ally, Austria-Hungary, leading to an escalation of the conflict into a broader war.
c) France's Role: France, as an ally of Russia, began to prepare for war in anticipation of the conflict. When Germany declared war on Russia, France found itself drawn into the war due to its alliance commitments, ultimately declaring war on Germany shortly after the conflict began.
This chain reaction of alliances and military mobilizations among the nations turned a regional conflict into a global war, involving multiple countries across Europe.