Battlefield Earth (2000)

Factual error: Amongst the essential parts of a nuclear weapon's detonation mechanism is a radioactive isotope of tritium, which has a half life of just 12 1/2 years. The tritium in every nuke on earth has to be replaced every ten years or so. This is by no means unusual; there are other perishable parts including detonators made of conventional explosives which would be completely inert after a thousand years. After lying dormant with no maintenance at all for that amount of time the nuclear weapons the 'Man-animals' find would be big shiny paperweights and not much else.

Ker: I don't know what you're so down about. You still get to be head of security, which, from what I can tell, is a pretty cushy job.
Terl: Well, I can assure you that I was not groomed since birth to have some cushy job that even a moron like you could perform. While you were still learning how to spell your name, I was being trained to conquer galaxies! To do anything less is a disgrace to my entire family line.

Trivia: John Travolta made the film with Franchise Pictures. A few years after the film, it was revealed in a court case that Franchise had fraudulently overstated the budget of Battlefield Earth by $21 million to scam investors. After losing the case, Franchise filed for bankruptcy, and Travolta fired his manager, who set up the deal with Franchise in the first place.

Question: Why are certain areas of the Earth irradiated? What happened?

MovieBuff09