JLPT N1
～を境に（をさかいに）
since; from that point on (indicating a major change)
Structure / Usage
Noun + を境に
Example Sentences
あの事件を境に、彼の性格が変わった。
Since that incident, his personality changed.
三十歳を境に、体力が落ちてきた。
Since turning 30, my physical strength has been declining.