The sharp economic downturn that occurred after World War 1 was a ?

The great depression

Explanation:

The Depression of 1920–1921 was a sharp deflationary recession in the United States, United Kingdom and other countries, beginning 14 months after the end of World War I. It lasted from January 1920 to July 1921. The extent of the deflation was not only large, but large relative to the accompanying decline in real product.

the tallest building in the western hemisphere and the sixth tallest building in the world