How did the course of events go from being a local conflict to war in WW1?

World War I began as a local conflict between the Austro-Hungarian Empire and Serbia in July 1914 and subsequently escalated into a global war involving all of the great powers of the time. The course of events that led to the escalation can be summarized as follows:

1. Assassination of Archduke Franz Ferdinand: On June 28, 1914, Archduke Franz Ferdinand of Austria, the heir to the Austro-Hungarian throne, was assassinated by a Serbian nationalist in Sarajevo, the capital of Bosnia and Herzegovina (which had been annexed by Austria-Hungary in 1908).

2. Diplomatic Crisis: The assassination sparked a diplomatic crisis between Austria-Hungary and Serbia. Austria-Hungary issued an ultimatum to Serbia, demanding that it take action against the nationalist movement and allow Austrian investigators into Serbia. Serbia accepted most of the demands but rejected some, which Austria-Hungary saw as unsatisfactory.

3. Declaration of War: On July 28, 1914, Austria-Hungary declared war on Serbia, after its demands were not fully accepted. This action was backed by Germany, which had a strong alliance with Austria-Hungary.

4. Russian Mobilization: In response to Austria-Hungary's declaration of war, Russia, a Slavic ally of Serbia, began mobilizing its military. Germany viewed this as a threat and issued an ultimatum to Russia, demanding that it cease military preparations. Russia refused, and as a result, Germany declared war on Russia on August 1, 1914.

5. French and German Involvement: France, an ally of Russia, was obligated by treaty to come to Russia's aid in case of war. On August 3, 1914, Germany declared war on France. Germany also invaded neutral Belgium, which brought Great Britain, an ally of Belgium, into the war on August 4, 1914.

6. Global Conflict: The involvement of France and Great Britain brought their respective empires into the conflict, widening the scope of the war beyond just Europe. The war eventually spread to Africa, Asia, the Middle East, and the Pacific, involving countries such as Japan, Italy, the Ottoman Empire, and the United States.

Thus, what started as a local conflict between Austria-Hungary and Serbia grew into a global conflict involving multiple countries and spanned several years, resulting in the loss of millions of lives and significant geopolitical shifts.