My grandfather was born the year the Great Depression occurred.
The Great Depression affected many countries.
The Great Depression raised unemployment and even suicide rates.
世界 means "world" and 恐慌 means "panic" or "scare," so when you put them together you get a scare that made the entire world panic. This is how we refer to The Great Depression. It was caused by and subsequently resulted in everybody in the whole world panicking together about money.
This is a jukugo word that uses the on'yomi readings of the kanji. You've learned them already, so you should be able to read this on your own!