Final answer:
The breaking apart of couple dance in 20th century America was largely due to significant socio-cultural changes such as the changing role of women in society, the rise of individualistic forms of entertainment, and demographic shifts resulting from wars and other societal changes.
Step-by-step explanation:
A primary reason that couple dance broke apart in the 20th century America can be attributed to broad socio-cultural shifts. These shifts include the changing role of women in society, economic changes leading to different forms of individualism, and the advent of new forms of entertainment that changed traditional social patterns. Women, due to greater employment opportunities, information about birth control, and the ensuing social independence, were no longer confined to traditional family responsibilities.
This led to them experiencing greater equality in their marriages and more autonomy, which in turn influenced their participation in social dances. Moreover, with the rise of working-class entertainment such as music halls and burlesque theaters, where dancing was often a spectacle rather than a couple's activity, dance itself became a form of individual expression rather than a shared partnership.
Lastly, external forces such as wars and the subsequent demographic changes also played a role in altering the marriage landscape, which indirectly affected couple dances associated with traditional married life.