Read this and answer the question. If the question is unanswerable, say "unanswerable".

Worldwide prosperity changed dramatically with the onset of the Great Depression in 1929. The Wall Street Crash of 1929 served to punctuate the end of the previous era, as The Great Depression set in. The Great Depression was a worldwide economic downturn starting in most places in 1929 and ending at different times in the 1930s or early 1940s for different countries. It was the largest and most important economic depression in the 20th century, and is used in the 21st century as an example of how far the world's economy can fall.

What changed worldwide property drasrically?
the onset of the Great Depression