derailment
noun /diːˈreɪlmənt/
  /diːˈreɪlmənt/
 - [countable, uncountable] an occasion when a train leaves the track; the act of causing this to happen- the derailment of a passenger train
 
- [uncountable] the fact of stopping a process from continuing in the way it was intended to- the derailment of the peace process