Depends who wins doesn't it? Victor always writes history.
In my own opinion I think it's quite likely that as far as Europe is concerned the 'tipping point' may well be when the EU turned from a mutual trading organisation concerned with peace and cooperation with some centralised legislative powers to an organisation focused on federalism and aggressive expansionism which provoked it's neighbours.
I think the Eurozone crisis and the refugee crisis' and the exposure of inequalities in power within the EU that exposed (e.g. Germany has a lot more power than everyone else because they hold the purse strings) will also be key.
I suspect that the deliberate movement of the centre of politics further left since the 90s creating a lack of real centrist parties will be seen as creating a reaction which drove many to the far right and the ultimate cause of much of the strife we will face will be left/right conflict.
I think the growing gap between rich and poor and falling living standards in Europe will cause huge issues in Europe which will further drive people to the extreme left/right.
Basically I think in Europe it will end up like every other war where attempts to build a European Empire fail (as per usual) because they cause rising nationalism. And also because of conflict between left and right wing ideologies.
And loads of us will get killed then we'll all realise how stupid war is and agree to have some nice middle of the road sensible policies we don't have to fight over.
And we'll carry on like that until the generation who actually remember how awful that war was are nearly dead and the next generation of idiots start the whole cycle again.
But yes, Empire building in Europe and high levels of conflict between extremes of left and right never ends prettily on this continent.
And it will be a world war because we will get dragged into a China/USA/Russia conflict sparked by North Korea which is the real deal, not N Korea itself.