watershed
n. countable C1 Advanced US //ˈwɑtɝˌʃɛd// UK //wˈɔːtəʃˌɛd// wa·ter·shed
n. a very important event or moment that changes how things happen in the future. You use this when a decision or discovery leads to a new era.
n. a critical turning point or decisive event that marks a significant change in a situation or historical period. Metaphorical extension of the geographical term; used in formal and journalistic contexts.
The invention of the internet was a major watershed.
The peace treaty marked a watershed in the region's long history of conflict.
Historians regard the fall of the Berlin Wall as a watershed moment that reshaped global politics and ended the Cold War era.
From water + shed. A calque of German Wasserscheide.