The A bomb did not exist back in 1940 Had it existed, it may have aleviated problems back then.
When the US was the only country to have the A-bomb, was such leverage used to blackmail other nations?
Every leap in technology coiuld be termed aggressive because it generates an advantage for the person that has it. the difference is in how it is applied.
Gunpowder, Armour, elephants, galleys, artillery, aircraft, submarines, chemical weapons, missiles, etc
All were develop and provided an advantage to the user when the opponent did not have such capability
It's easy to confuse different situations. Many things were different in 1940 than they are today.
You may not know or may have forgotten a darker side to the period when we only had the bomb, when a major political faction did call for us not to blackmail, but to obliterate China and/or the USSR before they could do anything about it. Coincidentally, it was a democratic president who said 'no' to these forces, just as Gore would not have invaded Iraq.
But part of what you are not recognizing are the things that change. Our nation at its founding, with Washington warning us to avoid any foreign entanglements, is a far different culture than one today where we are the world's leading military power, with over 700 bases in other nations (and zero other nations' bases on our soil, of course).
THe old saying is 'power tends to corrupt, and absolute power tends to corrupt absolutely'. While the US may be the best nation on earth for having a lot of power, it's not immune to that corruption, and we should think long and hard about the 'unlimited' power the nation is pursuing. I don't think we're ready to use it well, and it's a high risk to bring tyranny.
It's a little funny that people using the name conservative are in such a race to make the more powerful government in world history more and more powerful. I think we need to stop those efforts now, and pursue a peaceful balance of power, rather than invite a pre-emptive attack by others and try for utter world dominance.