World War I was much more destructive than any of the previous conflicts, because of the technological, military doctrinal, complex alliances, and assassinations.
*If any of the choices have these, choose it.
Technological: While most technology produced just before and during WWI was said to be "the weapon to end the war", it really only made it easier to murder people in larger numbers. Some example of Technological advancement can be seen in: Machineguns, which was created to be able to shoot large amounts of lead in a relatively short amount of time, resulting in large amounts of casualties in most cases. Another example are tanks, which were essentially armored cars with multiple machineguns. The US introduced the rotating turrent when they entered the war, which would then evolve to the type of tanks we are used to seeing today.
Military Doctrine: The Military took a different approach from before. Instead of doing strategic maneuvers on the ground with support, they essentially turned towards usage of trenches, which were complex, often zig-zagged half tunnels that spread across most of Western European mainland. They were usually fortified using wood and barb wire, and were used to protect soldiers. They were especially good for defense, if the enemies decided to cross no-mans land.
Complex Alliances: One of the reasons that World War I truly went global, without complex alliances, at the most Austrio-Hungary & Serbia would be at war with each other. However, with the alliances, countries generally declared war in support of their allies, leading to what is truly a global war.
Assassinations: The Spark that set off the war. Over the year, Serbia & Austrio-Hungary were constantly uneased by the fact of disputed land, in which each claimed for themselves. The Assassination of Austrio-Hungary's Archduke Ferdinand & his wife Sophie by the hands of the Black Hand Society led to the start of the war.
~