What are the most important themes that run through both Chapters 17 and 18 in Howard Zinn's "The People's History"?

One of the most important themes in Chapters 17 and 18 in A People's History of the United States is that individual action can have profound effects on social and political policy.

In chapter 17, Zinn focuses on the "black revolt of the 1950s and 1960s."  He is very direct in how he opens the chapter.  Zinn details how specific writers and thinkers viewed the racial divide that defined America.  The impressions of Countee Cullen, Langston Hughes were matched with the organizing efforts of Angelo Herndon and Hosea Hudson.  In each of these perceptions, Zinn makes clear that in order for sweeping social and political change to take place, individual action was needed.  Zinn views the Civil Rights struggle in terms of action vs. inaction.  Zinn's narrative focuses on inaction of government and those in the position of power against those at the bottom rung of society who seek to create change.  He details this theme with examples of student sit- ins and protests, "Freedom Riders," and stories of how individual action was critical to change.  Zinn does not suggest that legal equality in the form of Brown vs. Board of Education or efforts from the Kennedy Administration created lasting change.  Rather, he suggests that change was created through individuals displaying power from the bottom up in the form of the Civil Rights Movement.

This theme of individual action bringing about massive change is continued in Chapter 18.  He emphasizes this in his opening to the chapter on the Vietnam War:

From 1964 to 1972, the wealthiest and most powerful nation in the history of the world made a maximum military effort, with everything short of atomic bombs, to defeat a nationalist revolutionary movement in a tiny, peasant country-and failed. When the United States fought in Vietnam, it was organized modern technology versus organized human beings, and the human beings won.

When Zinn writes "the human beings won," it is a reminder of how individual action is critical to creating change.  In Chapter 18, Zinn makes the argument that the geopolitical control was underlying American action in Vietnam.  He does this by citing memorandum that affirmed the importance of the "domino theory," and through detailing how American interests were protected through intervention in Vietnam.  Yet, Zinn also discusses how American opposition to the war arose through individual action. Journalists such as Seymour Hersh in reporting about the My Lai massacre sought to increase public outrage towards the war.  Zinn also talks about how Vietnamese citizens saw the battle as one of national identity.  They did not see it as a geopolitical struggle against Communism.  Rather, these individuals saw their own nation's freedom threatened with American action in Vietnam.  In these examples, Zinn affirms the theme of individual action creating lasting change because American victory in the region became "impossible."