You'll probably have more luck by googling the event, as opposed to asking people here. At least, you're more likely to get the facts straight.
But in short, the bombings of Hiroshima and Nagasaki impacted the world because it was the first ever use of nuclear weapons in a war setting and it put the US in a new position of power, as they were the only country to ever have used nuclear weapons.
The U.S. dropped atomic bombs on another country for the first and only time when Harry Truman was president. So the lesson we should learn is that if that if we ever elect a president whose last name is spelled similar to "Truman", then we'll probably have the same thing happen again.
