What was the effect of Columbus sailing across the Atlantic? Maybe nothing! Maybe another sailor would have come 20 years later and American history would have played out just the same with different dates.
Or would two decades of Aztec rule made a difference? Two more decades of Nagualism before the Church started eradicating the libraries and the language? Could books have been copied and hidden? Would political bodies have had more time to adapt? Were there tipping points on the horizon?
Or was America in a steady state just waiting for Europe to come plunder it? Are forces at play which are so much bigger than individuals that nothing we do really matters?
Personally, I think it all matters very much. History does not repeat itself, it’s a story built on every word that came before it. Brexit will frame everything that comes after it, and if we had swapped this decade for a different decade in UK history, we would have a very different story.
Was the Korean war a major war in your book? To the Korean people it was.
In that war, the US's having nukes did not prevent North Korea from starting the war, did not prevent the Soviets from sending MIGs with Soviet pilots against the US army and air force and did not prevent China from sending a million soldiers.
Alternatively, do you claim that the fact that China at that time lacked nukes somehow emboldened China whereas if they had had nukes, they would have hesitated?
MAD means we probably won’t have a major war any time soon, so we’ll be trading with the EU regardless, it’s all semanitics and minor politics.