Question

what were the immediate causes of the 1st world war

Answer 1

Assassination of Archduke Franz Ferdinand

Answer 2

While @CHAD159753 is correct, it is important to understand the causes that lead to such tensions that lead to the assassination of Franz Ferdinand.

Europe was extremely nationalistic, and millitirazation of the continent had already taken place, creating tension and instability. On top of this, there were a dizzying myriad of alliances, consisting of two main groups. The "Triple Entant" consisting of the UK, France, and Russia. The other group was called the "Triple Alliance" (do NOT confuse with the "allied" powers of WW2), consisting of Austria-Hungary, the Ottoman Empire, and Germany.

The situation in Serbia was basically during this time, all big multi-ethnic empires were falling apart, after seeing that many countries became independent in Europe after revolutions, they decided they could do the same. This caused tensions in the Astro-Hungarian Empire, with the Serbians of Astro-Hungary wanting to become independent or part of a Yugoslavia. The murderer/assassin was from a basically, terrorist organization called "The Black Hand" that urged for the southern part of Astro-Hungary to break away and form a Yugoslavia. So when the Archduke was visiting that area, it was only logical that they assassinate him. Now when this assassination occurred, Astro-Hungary freaked out and invaded Serbia, who was allied to Russia, and Russia had to step in and defend Serbia. Now, Germany was a part of the Triple Alliance, and ally to Astro-Hungary, and had to defend/assist Astro-Hungary. From here, many other nations were obligated to enter WWI because of their alliances/treaties, and we fought a very, very, bloody war.