I don't know exactly when it started, maybe when the Stutsnex virus was inserted into an Iranian computer. Since then Russia, China, and North Korea have all been attacking western military and civilian systems on a daily basis. If that isn't war, I don't know what is.
100 years of peace before WWI?
Not sure if that is accurate.
The only way to avoid war would be a global economic reset. And no one is going to do that.
Europe between the fall of Napoleon in 1815 and the Great War of 1914-1918 (WW1), was hardly a peaceful place. Wars and revolutions raged constantly. The 1840s saw revolution in France. There were wars between Prussia and Denmark, Prussia and Austria, and the Franco-Prussian war of 1870 which resulted in the creation of the German Empire. The Italian peninsula unified in a series of wars into the Kingdom of Italy. Prussia, Austria-Hungary and Russia split up Poland (Duchy of Warsaw). Add in all the colonial wars and you have a pretty violent place. It only seems peaceful when compared to the 20th century’s European wars.