Incident
noun
An occurrence that causes change somehow can also be called an incident. 事変 is a formal word for big, unexpected incidents that are disruptive and chaotic. This can involve natural disasters, sudden riots, or other large-scale disturbances that need military intervention. It can also refer to unannounced warfare. You'll most likely see this word used in names for historical events, like the Manshuu Jihen (満州事変), or the Manchurian Incident. The 変 kanji suggests "change," so you know 事変 is only used for historical incidents big enough make things change!
じへん
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.
上海事変は何年に起こりましたか。
What year did Shanghai Incident occur?
私は東京事変というバンドが好きです。
I like a band called Tokyo Jihen.
この事変は、中国では九一八事変として知られています。
This incident is known as the Mukden Incident in China.