One thing you definitely should consider in thinking about this topic is what kinds of "challenges" you are interested in pursuing/discussing/exploring. Sure, you can discuss the global political challenges associated with the Cold War, but you might also look at social and cultural historical factors that had an impact on the post-World War II world (in this case, I am thinking most specifically about the United States). One way or another, you need to narrow your focus. One thought that I have is about the rise of modern civil rights movements of various kinds and how they had a deep and dramatic impact on American society between 1946-1974, including but not limited to:
--the Women's Rights Movement
--the Civil Rights Movement (African Americans)
--the Gay/Lesbian Rights Movement
--the Latino Rights Movement
--the Native American Rights Movement
And the list goes on.
Another important factor to consider when looking at the years you have outlined--1946 through 1974--is the emergence of the "Baby Boom" generation and their resultant enormous impact on American society and culture. They, the Baby Boomers, were directly involved with and in many cases responsible for the seismic shifts that occurred in American society through the many movements listed above. This generation has had (and continues to have) tremendous influence on American society--socially, culturally, economically, and politically.