The United States is not just the country with the largest arsenal of nuclear weapons. They also happens to be the only country on earth who have used nuclear weapons against civilians. None of the other countries, including the former USSR and North Korea have used nuclear weapons on civilians, despite having the capability to do so. And I still remember the sanctions and embargoes imposed by these hypocrites in 1998, when India tested nuclear weapons. And they invaded Iraq claiming that the latter was trying to develop nukes.
And was that done for worse? You ignore a lot of facts and truly make a conclusion that is purely based on emotions instead of real facts and real threats. And I talk about Japan in this case.
One sure thing is that the USA demonstrated its power by using nuclear weapons in Japan but it was not only done for that purpose.
The emperor was considered a god in Japan. Religious fervor for the God-emperor was an unimaginable motivation and stimulus for Japanese society and soldiers. WW2 was a Holy War for the Japanese people. Japanese were very fanatic and were willing to sacrifice everything to achieve their aim, they were happily willing to sacrifice their own lives without an eye blink, About 3800 Japanese pilots flew suicide attacks for the Empire of Japan. This is not the end, they also thought that Americans were very soft and weak. If the USA dropped nuclear bombs into the sea and didn't harm civilians, do you really think that the Japanese would stop? No, instead, it would amplify their thought that Americans were soft. The real use of nuclear weapons on them showed the Japanese that Americans weren't that soft but definitely, this wasn't the only reason for their surrender. Even one atomic bomb alone was a weak reason for them two stop, even two weren't enough but at the same time, the Soviet invasion and some other factors truly showed the Japanese that they were standing no chance to win the war.
Also, In 1944, 99% of Japan's GDP was a military expenditure. Hiroshima and Nagasaki were important locations for the Japanese military industry.