Read this sentence from "The Most Dangerous Game" by Richard Connell:

After the debacle in Russia I left the country, for it was imprudent for an officer of the Czar to stay there.

What is the meaning of the word debacle in this sentence?

Debacle is a sudden and violent collapse. The "debacle in Russia" refers to the Russian Revolution of 1917. Thus the time period of the story is the five or six years between 1917 or 1918 and 1923, a time at which Russian Communism reduced the privileged life of the noble to a level at or near the life of the Russian proletariat.