first contact, advanced alien ships appear over Earth's cities 
 they remain mysterious and remote, but monitor populace and communicate via UN and do share technology to eliminate any shortage of humanities basic needs 
 impact includes major reduction in crime, edict against animal cruelty, move towards a single nation world. 
 stifles scientific progress (pointless in the face of race so much more advanced) and art 
 most people seem to rotate between extended education and gap-year type work experience. 
 also appear to have monitored earth for millenia, putting a damper on most organised religion (seems a bit unrealistic how completely, painlessly and quickly this occurs) 
 (view spoiler)[ultimately they are here at the behest of a galaxy-spanning over-mind which sees the potential for transcendence in humanity 
 they guide humanity to the point where this transcendence can occur in the population under 10, 
 remainder of humanity live out their lives, ending the race... (hide spoiler)]