Probably the first war.
Where it was demonstrated that you can achieve your geopolitical goals through the ruthless application of large scale violence.

Most “pivotal” in terms of what?

The First World War ended a long period of peace in Europe, revolutionized military thinking, saw the communist takeover of Russia, the emergence of Japan as a modern military power, and the shift in US policy from isolationism to intervening in a European war.

The Second World War involved even more death and destruction, nuclear weapons, and led to many changes in international relations thereafter.

There are some ancient wars that shaped what Europe ended up being like, which in turn shaped the eventual thinking and culture of Western Civilization. There are some conflicts in China and Japan that could also have changed what those civilizations became like. Etc.

@Zaku

Pivotal in the sense that we now live in a world that decisively emerged from the conflict you see as most pivotal.

Obviously WWII seems to beg for this title, but as @ragingloli mentions, it could be a more historical war that led to that sort of major conflict. Napoleon’s conquests seem to lay the groundwork for such a modern war machine.

In the USA it would be the Civil War:

with 750,000 dead

brother fighting brother

the rich could avoid the war; buying their way out.

Impossible to answer. The Trojan war (12–14 BC) made a difference to all that came after.

Norman Conquest in Europe

Thirty Years War (1600s)

Revolutionary War (1776)

WW1 and WW2

all of these had huge consequences that changed the world as a result.

In my mind, it’s impossible to pick just one because the built on each other.

I’m leaning towards WWI. It was a shift in human history in how wars were fought and took dehumanization to a whole-new-level. It saw the introduction of toxic gas, flamethrowers, mechanized warfare like tanks, airplanes, barbed wire, mortars/artillery, trench warfare. If you look at the period’s art/music/dance/poetry etc. there was a profound shift as well. It’s when dissonance in music was born, surrealism, off-rhymes intentionally warping the traditional poetic forms like sonnets, etc.

WW2 is the obvious alternative with nuclear weapons and genocide being the most extreme changes.

The advent and subsequent offensive use of nuclear weapons was the most consequential moment in warfare.

I think it was completely unique to WWII’s era, and not so related to the outcomes of past wars that it must be viewed through the prism of prior wars.

I thought of the question because it struck me that the American Civil War had such a huge impact on the future. I wondered, which war had the biggest impact.

I“m going to go with the Greco-Persian wars. Had the Persians prevailed and not the Greeks then Alexander may never have come to pass a hundred years later, and even later, the Roman empire.

The war between the Persians and Greeks approx 500 BC
It defined the difference and conflict between East and West.
The conflict continues to this day.

Exemplified by the Battle of Marathon

The one is which your child died.

It’s what I call The World War.
What WWI ended up as set the stage for WWII so I consider it one world war instead of two.

Sadly, I think it could be the next widespread conflict that’s brewing right now. It may just reset civilization back to zero.

Edit: “in which”

@janbb You might find this hard to believe, but I didn’t catch that. ;-o

@TJFKAJ is correct. The Battle of Marathon is probably the single most consequential battle in Western European history.

In my mind it has always been the First World War that had the greatest consequences. It was the first war in which the entire planet was involved. It was the first industrialised war that mobilised entire economies in support of a war effort. It upset the old social order and far from resolving anything its unjust settlement led to a second world war just 20 years later. We can only dream of the world we would have had the First World War never been fought.

The first war . Og verses Krug. In 10,000 BC.