@Khandro
The Branagh-narrated series about WWI is uppermost in my memory. They had a go at explaing the causes but the lasting impression I have is that it was practically a grotesque parody of the (later) board game of Diplomacy, whereby lasting piece had been achieved through a complex web of mutual-support pacts. Germany being allied to (Ottoman) Turkey being one bizarre setup with slight echoes in the present day.
Anyway, the Serbs hated being ruled by Austria-Hungary, send in their patsy to shoot the Archduke, the Russians mobilise to support the Serbs, so the Germans mobilise to support the Austrians and the French are allied with Russia, to keep Germany in that two-front vice which has been its problem ever since it called itself the Holy Roman Empire.
The resurgence of Rome is in Revelations, innit? A pity it wasn't a 27-headed beast, eh?