To impoverish is to take away a person's livelihood. When a drought ruins a farmer's crop and he has nothing to harvest, his bad luck may leave him and his family impoverished, or poor.
The Latin prefix in- is changed to im when in front of a word starting with the letter p-, but its meaning "in" or "into" stays the same. With roots in the French word povre meaning "poor," impoverish means to make poor or drive someone "into poverty." The 2010 earthquake in Haiti left over a million people impoverished, destroying everything they owned.