Answer:
Convinced that Austria-Hungary was readying for war, the Serbian government ordered the Serbian army to mobilize and appealed to Russia for assistance. On July 28, Austria-Hungary declared war on Serbia, and the tenuous peace between Europe’s great powers quickly collapsed.
Within a week, Russia, Belgium, France, Great Britain and Serbia had lined up against Austria-Hungary and Germany, and World War I had begun.
World War I brought about massive social upheaval, as millions of women entered the workforce to replace men who went to war and those who never came back. The first global war also helped to spread one of the world’s deadliest global pandemics, the Spanish flu epidemic of 1918, which killed an estimated 20 to 50 million people.
World War I has also been referred to as “the first modern war.” Many of the technologies now associated with military conflict—machine guns, tanks, aerial combat and radio communications—were introduced on a massive scale during World War I.
The severe effects that chemical weapons such as mustard gas and phosgene had on soldiers and civilians during World War I galvanized public and military attitudes against their continued use. The Geneva Convention agreements, signed in 1925, restricted the use of chemical and biological agents in warfare and remains in effect today.