The United States restricted the amount of European immigration done, they weren't participating or even a part of the League of Nations, and people were just tired of getting to foreign wars as a whole. Only 150,000 immigrants per year were allowed to immigrate to America in 1929.
To stop ethnic cleansing of Muslims and Croats.
Answer:
Matthias Jakob Schleiden was a German botanist and co-founder of cell theory, along with Theodor Schwann and Rudolf Virchow