Why can allies of the US have Nuclear weapons without any threats from the US and other countries cannot have them?

The US and allies of the US can have nuclear weapons while other countries do not because of one golden rule:

-The best predictor of future behavior is by studying past behavior

While all countries have played their part in destruction and war over the centuries,

Countries such as Iraq and Saudi Arabia have been aggressors, broken treaties with other nations, and ignored basic international laws within the last 30 years.

If you are unable to trust a country, there is no way any nation in their right mind would approve and support the creation of something so powerful and potentially harmful.

BUT: If you look at the past behavior of United States, it is well known that US is the ONLY country to have used nuclear weapons during war, killing millions of civillians.

For that, US is the only county that SHOULD NOT have nuclear weapons since everybody is "unable to trust" that country (with good reason).