People can and do own tanks. Since they are giant (hard to park), slow moving, consume a lot of fuel, tend to need expensive maintenance, and can't be operated

People can and do own tanks. Since they are giant (hard to park), slow moving, consume a lot of fuel, tend to need expensive maintenance, and can't be operated on many roads due to weight / vehicle restrictions, few people want to do this. As far as nuclear bombs go... there are restrictions on owning fissile material in general that would preclude owning enough to have a working bomb.