confluence         
noun [ C ]  geography specialized uk/ˈkɒn.fluː.əns/ us/ˈkɑːn.fluː.əns/
 (河流)汇合处,汇流点,交汇处
the place where two rivers flow together and become one larger river
  汇集,集合
a situation in which two things join or come together
  The change has been brought on by a confluence of factors. 这种变化是由多种原因共同促成的。 
 A confluence of events is pushing nuclear policy into the national spotlight. 一系列事件促使核政策成为公众关注的焦点。