The International Space Station (ISS) does not present a nuclear or likely collision threat that we know of, but it remains one of the most dangerous objects in orbit because of its size. Collisions are possible with any space object, but any such accident with the space station could create a doomsday scenario involving space debris that is proposed by the Kessler syndrome.
In simple terms, this means that an object striking the ISS might cause a cascading effect of other such accidents from all the resulting debris. At some point, there would be too much debris for us to continue with certain space activities, possibly for generations. As recently as 2017, objects have detached from the station and now have the potential to crash into the ISS.
The station is also a danger to the astronauts who work aboard it. There have been several problems with the oxygen generators, carbon dioxide removal systems, environmental controls, the central computer, electrical and power systems, torn solar panels, and ammonia leaks. If one of these problems turned into a catastrophe, the ISS could quickly become a serious danger as it fell to Earth and collided with other satellites and debris along the way.