The appropriate response to the question regarding why the setting of New England in 1866 is important to the structure of the play is:
The Civil War had just ended, and the North was a safer place than the South for women who were fighting for voting rights for all.
This answer accurately captures the historical context of the time, highlighting how the aftermath of the Civil War created an environment in which women's rights activists could advocate for suffrage more freely in the North compared to the South.