Because Slate was more common in wet microclimates.
Hope I Helped :)
One of their biggest arguments was whether or not the USA should join the League of Nations
Answer:
The Bombing Of Pearl Harbor
Explanation:
In 1941 isolationism was put mainly to a stop when japan bombed pearl harbor. Many Americans felt outraged and angry, many activists for isolationism now supported the war effort like Charles Lindbergh.
(I studied this topic for NHD)