Didn’t the british constructed Entente use serb assasins to bring about WWI?
No. When the Muslim Ottoman Turks left after 400 years of tortuous occupation, they handed Bosnia over to the Austro-Hungarian Empire. Naturally, the inhabitants of Bosnia resented exchanging one form of enslavement by a foreign ruler for another.
There were actually several attempts on the Archduke Franz Ferdinand's life that day, but the one that happened to succeed was by a Bosnian Serb anarchist, who had nothing to do with Serbia.
Still, the Hapsburg's knew that sooner or later , Serbia would try to free Bosnia from them, and the Austrians thought that this was an opportune time to take Serbia on because Serbia hadn't yet recovered from the Balkan Wars. Austro-Hungary used the assassination of Ferdinand to start a war with Serbia. Germany joined them, and the whole thing spun out of control as other countries took sides.
Even before the assassination, Europe was already a political tinderbox. Austro-Hungary's war on Serbia was just the spark that lit the flames of WWI.
It was kind of ironic, because none of the Hapsburgs liked Franz Ferdinand as his wife wasn't up to their breeding standards. That's why Ferdinand had to take Sophie to some outpost Hapsburg colony like Bosnia to get any attention and recognition as a royal. And then what happens? They die. But the attention and importance that Franz Ferdinand and Sophie never got in life, they got by their deaths.