Oh please - France was looking for any excuse to go to war and retake Alsace-Lorraine and get payback for Sedan, Russia was all too happy to rattle sabres whenever the question of panslavism was raised, Britain wanted to take Germany down before it could build a large enough navy to threaten its naval superiority etcetera etcetera. Telling me that Germany was the only country with unhealthy levels of jingoistic nationalism is clearly not supportable.
I wouldn't have said that France was looking for an excuse to go to war, exactly. Sure, once the war started, everyone was certain they'd be in Berlin in a week, and it was a motivator to action, but if they were looking for any opportunity, why did they take the numerous ones that came up in the years preceding the war?
As for the Russians, as you point out, it was not nationalism, but pan-nationalism. They didn't want to go to war because they were Russian, and they didn't really want to go to war at all, IIRC, but felt forced into full mobilisation by AH's flagrant breach of Serbian sovereignty.
And the British wanting a powerful navy was not the result of jingoism. It was the result of the simple fact that Britain could not be attacked without crossing the channel. Naval superiority was the key to Britain's defence, and whilst it may've been an object of nationalist pride, it was not designed for that reason.
As for AH, perhaps it didn't even have anything to do with nationalism, so much as wanting to keep their empire preserved.
But Germany, you could argue, was more militaristic, and therefore more willing to go to war. They wanted their 'place in the sun'. They thought they were superior and so deserved this. Maybe it wasn't an immediate cause of the war, but it could be put down as one of the root causes.
It also firmly believed that Germany deserved much better than what the system was offering to it. You know, more colonies, bigger navy, it's own place under the sun etc.

Germany was simply not satisfied with its position - and I can understand why.
Wow, I hadn't even read this when I wrote that last paragraph.
This thought that they didn't have what they 'deserved' is nationalism. They 'deserved' it because they were better.
Balance of power doesn't mean that the relative power of certain actors doesn't change. When one country gets too powerful, other countries form alliances against it.
In that case, it is obvious that the balance of powers could not be preserved. Nations changed in power, and were changing in power. But I would say that the balance of power is the name given to the attempt to create a situation of opposing, yet equal, blocs. And in this attempt, countries varied in power, leaving it as just an attempt, and not a completed goal.
The problem is that countries are not entirely rational actors and they don't always have all the information to make a good decision - sometimes they believe that the enemies are weak when they are not, underestimate them and thus start a devastating wars.
Every nation thought that the war would be over by Christmas. So, every nation held this false belief of clear superiority. And, due to this, whether the balance of powers was actually balanced or not, a war would have started soon after 1914 when one power saw another catching up to it. They would take their advantageous opportunity whilst they could.
Germany did not initiate a world war. Germany believed the Austro-Serbian war could be localized. It was a combination of their own blunders and of France's policy that turned the war into a global one. If anything, the diplomatic balance was uniquely against Germany in 1914, a constellation that France knew was unlikely to get any more aligned in the French government's favor. Things were very likely to get better for Germany in the long run, not worse.
There is a quote somewhere by someone, I think, von Moltke, that said that it was the time to strike, because Germany would just get weaker. And before you ask, I don't have it on me. So, I have no evidence, but I quote I can't quite place.