Are you implying that a particle accelerator can be weaponized?
Who knows what it could lead to. But no I'm not implying that there is any great danger from this project, but I'm objecting to the idea that one party gaining exclusive information somehow leaves the other parties in an unchanged situation.
Probably not. We're doing a lot better than we were 100 years ago, and nuclear weapons have been a great deterrent to stop many countries from engaging in wars that they might have been more tempted to if at least one of the parties didn't have nuclear weapons.
We've had almost constant small-scale proxy wars instead, and the arms industry isn't exactly going through hard times.
More realistically, we got lucky and barely dodged the armageddon bullet on a number of occasions.