The various pacifist strains of the late 1950s and early 1960s converged in the hippie movement of San Francisco. The hippies celebrated their first "Summer of Love" in 1966 while Huey Newton, Bobby Seale, Angela Davis and other black activists founded the "Black Panther Party" in nearby Oakland, one of the most visible groups creating a season of urban violence. There were racial and political riots for the rest of the decade, culminating in the assassination of Martin Luther King (1968). Meanwhile the Vietnam war become more and more unpopular, especially after it was learned that USA troops had massacred more than 500 civilians at My Lai. Public opinion was feeling disenfranchised from the political system. The dissatisfaction was best represented by the demonstrations at the Democratic Convention of 1968 in Chicago: that turned out to be a key event in the evolution of the USA democracy. After 1968 the parties became more democratic (primaries became the standard method of picking candidates, thus replacing the party machines that had previously dominated politics) and referendums became more commonplace.
The counterculture didn't rely on computers and social media, which didn't exist at the time, but was nonetheless able to mobilize masses. Activists communicated very effectively using telephones, print media, posters, flyers, bulletin boards and word-of-mouth, especially on campuses. For example, the Pentagon of October 1967 demonstration was huge: over 100,000 participants. A large number were college students.
Feminism was making inroads, and in 1969 Sylvia Rivera opened a new front in the civil-rights movement by founding the "Gay Liberation Movement".
In Europe all these problems were given an ideological twist. The student riots spread to West Berlin in 1967 and then to Paris in 1968. Student demonstrations forced Charles DeGaulle to resign in 1969. Leftist students and leftist unions led Italy into political chaos.
Nonetheless, the USA won the "space race" in 1969 when Neil Armstrong became the first man to set foot on the Moon. It is debatable whether that event marked the beginning of an era or the end of an era.