AsWe have been warned that our planet wouldill be ruined many times over if all the nuclear weapons in the former Soviet Union and the USA detonated simultaneously.

AsWe have been warned that our planet would be ruined many times if all the nuclear weapons in the former Soviet Union and the USA detonated simultaneously.

I'm not sure who you are indicating is being warned, but I will assume it is 'everyone' so I will use 'we'.

I have a question about AI and nuclear weapons, w. Which one is more powerful?

These are two separate statements so they can either be separated by a period and capital letter or semicolon.
Semicolon - 'nuclear weapons; which one..'

Personally, I prefer the former over the latter.

'Prefer' typically means you 'like' something over another. If you are indicated that you believe this statement, it sounds better to say: 'Personally, I believe it's the former over the latter.'

Because AI can control nuclear weapons while the latter doesn't know how to control AI.

When you are continuing a thought from a previous statement, 'because' shouldn't be used. You could combine it with the sentence before or take out the 'because'.
It might sound better to say: 'AI can control nuclear weapons but nuclear weapons can't control AI.'