To the best of my knowledge it's A
The thing which was a major factor that threatened the major unity in the United States in the mid-19th century was:
<h3>The Great Depression</h3>
This refers to the period around 1929 in the United States which has a profound effect on the national economy.
This led to the failure of many banks, increase in unemployment and high deflation rates which all threatened the national unity.
Read more about Great Depression here:
brainly.com/question/441267
The new approaches to form that the impressionists introduce were:
-Color theory (in light and nature)
<span>- added brown or black color</span>
-Object shadowing
- <span>'en Plein air' (painting outside)
</span>
as for the post-impressionist, they still adopted these techniques, but they add more emotion and personal insight into their artwork.
