Trying to understand the origins of the 20th century world war

I would have thought that you don't attack another nation until they attack you or, when it's obvious, they are about to attack you.  Was the latter  the case with Israel when they launched their war in 1967?

We broke that principle when we declared war on Germany in 1914 and 1939 but, on both occasions, an obedient German people, unthinkingly, followed two leaders who were out of control and somewhat deranged.  Therefore, both the Kaiser and Hitler had to be stopped.

In the case of 1914, however, our army was small with only seven divisions; we had not let Germany know that we had been in secret talks with France since 1906 that we would come to her aid if she was attacked by Germany; and, on the 4 August 1914, island Britain was not on the German list to be attacked when we attacked her on that date.  (sources: BBC History magazine Feb 2014, BBC documentaries)

Who has done the most subjugating?

Mr/s B Parsons believes that the EU is subjugating the UK.  We entered into it voluntarily after a referendum and send representatives to its Parliament every five years.
Over hundreds of years, the UK acquired domination and control over fifty countries by force of arms and kept them subjugated by military power.  We also controlled all the major sea lanes of the world.
All this set a very bad example to Germany that was very late in the game of conquering or claiming nations to build an empire.  Yet, remarkably, those fifty countries still fought for us to stop Germany taking our world control off us in 1914 and 1939 (better the devil you know than the devil you don't know).  To this day, the US/UK, with NATO, remain as the world's dominant power bloc.  Germany is the dominant partner in the EU and Angela Merkel of Germany is the highly respected senior partner in the EU - but, by constraint and not coercion.

Such a pity but worth it when we didn't have to die!

We rushed to war on 4 August 1914.
Our intervention was premature, our army too small and, certainly, war was unnecessary when Germany had no intention of attacking Britain - until we attacked them.
The Cabinet knew it would fall, then lose power at the General Election, if it did not declare war on Germany - according to historian, Niall Ferguson.
Our war, much of its prosecution and the way it was resolved in 1919 was utterly stupid, especially the reparations and all the blame laid on Germany alone.
Germany nearly won in 1914, 1916 and, once more in 1918.  The beat Russia in 1917.
Violence, domination and control breeds more of all three, as we have seen off and on in Ireland for 800 years, in Israel/Palestine for 70 years - and, with the UK with our mighty victory minus magnanimity in 1919 that led to the second half of the European/Christian World War - in 1939, according to a former Conservative leader, Ian Duncan Smith.
UK has been engaged in warfare, somewhere in the world, for every single year for the last 100 years. Finally, in 2015 it seems, we may, finally live in peace and non-violence with all our neighbours in the world.
Even with the knowledge that 10 to 20 million people died horrific deaths in 4 years, nearly all Brits today still maintain this was such a pity but very necessary to stop Germany taking over some of our world control in 1914.  In 1914, a Germany far more democratic than the UK, too.
This is not a good example to set to the Muslim extremists/radicals of this day.
Ours is not a fine record.