I would also challenge you to use BF's quote whilst walking the cemeteries and battlefields of Belgium and France, whilst reading the huge list of the missing without any know grave, remembering the 16 million + 54 million approx. killed in The Great War and WW2.
I've been.
I've also visited Belsen, and Auschwitz:
Peace at any price is too high a price.
Because if all the nations of the world sit around talking and turning their swords into ploughshares, you can bet that that at least one of them has other plans.
Liebensraum will ALWAYS be a rallying cry.
Then you should understand the absolute determination to avoid that happening again by fully contributing to a European Parliamentary system, and thus reduce the threat of nationalism.

The facts are previous systems failed terribly to avoid war of a magnitude that was almost beyond imagination.

All that the EU is doing is likely to lead to civil, rather than national, wars in the future. Different names, same suffering. I simply don't buy all this talk that the EU has prevented war. Maybe it is true in the case of Nato, but not the EU. The fact that no nation vs. nation war has occurred is down to other matters such as the relative prosperity of the West. To say that the EU has prevented wars is totally unprovable. History is littered with the carcasses of huge empires which have collapsed in a bloody fashion.
As for nationalism, it's one of the words that's always bandied about in a perjorative way to ensure that valued aspirations of pride in the freedoms, democracy and values of one's own country cannot be uttered, lest one is tarnished with an undeserved brush.
You are right Nick in quoting the UN in the context of international peace, and its achievement (so far) of keeping the majority of nations away from each others throats.
However, the worth of the EU cannot be undervalued, as it has been a major factor of keeping the EU nations in line and away from the international 'gun' (and I am not ignoring the Afghan situation!) which has previously been triggered, even under the so called control of the toothless League of Nations.
The prosperity of the West before 1914 was in fact the cause of the Great War, with the ability of the British and French empires able to engage in war against the German nation. All seemed to believe they could afford the human and monetary cost of international war, protecting their perceived imperial interests with no United Nations, League of Nations, or EU to enforce diplomacy. That is the diffence Nick with the contemporary era and then; we have international diplomatic control factors of both the UN and EU.
The cause throughout history of so many domestic, national and international conflicts have been the actual and perceived emotion that the protesting, rioting, people have no representation in a parliament or legislature of any kind. That is why the British people must pro-actively support the EU ensuring we have a say in the diplomatic process via our elected representatives.
Failure to do this will result in disenchantment: a feeling of disfranchisement from their destiny. It is therefore extremely dangerous not to encourage the British people to become fully involved, fully engaged, and democratically supporting, developing and enforcing EU policy for the good of all nations.
Civil War, as you talk of Nick, last took place in Britain due to a monach, Charles I, trying to ride roughshod over Parliament and the democratic rights of the people hard won from 1215 onwards. It is only by collectively working together in the UK Parliament, the EU, and the UN, that we can obtain our rights, defend the rights of others, and secure a long term peace.
The only danger to that is the breaking away of separatist, nationalistic groups, determined on their own self interested politically agenda, that can cause conflict and distrust away from the central European arena.