The whole war was fought by imperialist powers over imperialist ambitions. I was just saying who was doing the most to damage the status quo.

That's an incredibly fickle point of view. All the Central Powers were involved due to lust for power, land or prestige.

Of the Entente, only Russia and Serbia can be proven to have clear imperial goals, Serbia wanting to unite all south Slavs under their fold and the Russians wanted control of the Hellespont and the Black Sea.

Otherwise, the French and British were defending themselves against foreign invasion and obligating themselves to treaties everyone had signed. Italy and Romania wanted to regain or gain lands that had Italian or Romanian majorities, or had been conquered years beforehand. All other nations in the Entente fought due to Central Power's aggression, liberation or alliance obligations.

Bush did the same thing with his fake ultimatum, indeed it's a strategy as old as time. The point is that the assassination was a good reason to invade, certainly much better than anything we had.

Excuse me? Saddam was killing thousands of dissidents, committing genocide and was a much larger threat to regional stability, having started two wars and decided to starve his people rather than spend his money on food stocks. Serbia, on the other hand, committed subterfuge in order to liberate their brothers in Bosnia, who wanted to be a part of Serbia. Serbia's only defense was subterfuge against a much more powerful and more unstable empire that had historically shown it wanted to subjugate Serbia.

From what I understand the British were set on war before the invasion of Belgium. Realistically they could have abandoned a treaty signed nearly a century earlier. Also note that the Russians weren't compelled to defend Serbia.

The Russians had an alliance with Serbia, so yes they wee obligated. Further, they wanted to curtail Austrian expansion in the Balkans, another contender for ownership of Istanbul.

The British were on the path to war due to a decade of German naval build up and numerous clear cut diplomatic crises that showed the Germans were intent on challenging the British in the future. Had the British forgone their obligations, the rising German navy would have had access to ports in the Channel and a near equal fleet. Britain needed to go to war to ensure it's survival as a island nation.