From an Australian perspective, the wealth of modern Europe has been built up over centuries of development. Any tourist visit will only accentuate that impression, with grand buildings a thousand years old and art and technology dating back from before the "discovery" of Australia.
In one way, of course, this impression is absolutely true - regions like Flanders and northern Italy were economic powerhouses 600 years ago, and the slow accumulation of wealth over decades and centuries gives nations (and individuals) an unassailable advantage. This is why Black Americans have less wealth than white Americans after normalising for current income - even modern equality (if it were ever to exist) would not, by itself, wipe out the legacy of historical inequality.
In another way, however, this impression is quite misleading. Sure, you can walk around Brussels and see the 600 year-old city hall, and the Royal family has certainly built up its collection of palaces over the past 200 years. But these legacies of the past are the exception more than the rule. Modern Belgium has been built almost entirely over the past 60 years, on the rubble of the past. A very rich rubble, to be sure, but rubble nevertheless. Over 1% of the population of Belgium died in each of the two world wars (not unusual in western Europe, in central and eastern Europe figures over 10% are common), and the destruction of houses and infrastructure was much greater. Over 30,000 million tonnes of explosives fell upon Belgium during the wars, equivalent to more than a tonne of munitions per square metre of Belgian territory. Around a quarter did not explode, so even today ~200 tonnes of munitions are uncovered yearly by farmers and disposed of by the Belgian army.
This is the legacy of war, not only does it destroy what may have taken centuries to build, but it has the capacity to keep up the killing, long after the initiators have died. Even today Cambodia has 5 million unexploded landmines and hundreds of deaths every year. Anyone who advocates a war should first meet just a few of the 40 000 childhood amputees in Cambodia, who live today with the consequences of past decisions.