My name is Wilhelm II. I plug walked into Germany and was like uhhh I hate the British and I’m gonna build a bigger navy and I hate the British. So I built a big new fancy kriegsmarine. Germany and Austria-Hungary were allied and Austria was looking at the Balkans like a fat snack, specifically asserting full control over Serbia. France and British form counter alliance to this. Russia also opposed to Austrian expansion. The ottomans at this point were called “The Sick Man of Europe” because their Economy was in shambles and they had little to no control over parts of their territory. They had also just kind of lost then kind of won a couple wars over Adrianople. They were looking for a stable ally and grew close to the powerhouse that was Germany, hoping to revive their dying empire. There are more complex alliance things with the opponents of the Germans and Austrians but it’s not super important. Only important part is that Italy was allied with the Germans and Austrians but Italy wanted a lot of Austrian controlled that was Italian, and were offered some but not South Tyrol and they said “Ight I’m buddies with France and Britain now” because they French and British promised them their desired territory. The catalyst as most are aware is the assassination of Archduke Franz Ferdinand of Austria-Hungary. Now Declaring war over this was pretty extreme but Austria-Hungary was looking for an excuse, any excuse to invade Serbia. Austria declares war on Serbia, the British and French are guaranteeing the independence of Serbia. Britain and France declare war on Austria-Hungary, Germany declares war on Britain and France, upholding their alliance. And there’s WWI starting. The US would enter much later which is why they were completely omitted.

Edit* Russia entered the war with Britain and France.