How did nuclear weapons change American politics and foreign policy?

Nuclear weapons are a very dangerous technology, especially when multiple nations obtain them. The concept of Mutually Assured Destruction is very important in the affect of nuclear weapons on US Foreign Policy, because it was almost entirely what stopped nuclear war throughout the second half of the 20th century. Mutually Assured Destruction basically just means that if my nation fires our nuclear weapons, we will be met with equal fire that, when combined, will annihilate the world as we know it. American Foreign Policy was changed in that we had to be very careful with nuclear weapons because they create such large scale damage that it would be inevitable that some damage be inflicted back on us.