Don’t want to discourage any new answers but here is an absolutely fantasticanswer to a pretty similar question.

User who originally wrote it has since deleted their account, so I can't give them proper credit sadly.

https://www.reddit.com/r/AskHistorians/comments/2ukpr4/why_is_ww1_considered_the_first_world_war/?st=jns0yj30&sh=c7d53ca1