On a Wikipedia page, it says the following about the song American Pie:

Question

McLean likely wrote the lines in response to the May 4, 1970, Ohio National Guard shootings at Kent State University that killed four and wounded nine unarmed people at the scene of a demonstration against the U.S. military invasion of Cambodia during the Vietnam War. The phrase "not a word was spoken" refers to President Nixon's silence on the matter. Stanley Karnow noted in his Vietnam: A History that "The [Nixon] administration initially reacted to this event with wanton insensitivity. Nixon's press secretary, Ron Ziegler, whose statements were carefully programmed, referred to the deaths as a reminder that 'when dissent turns to violence, it invited tragedy.'"

Can someone please explain to me the part below?

While demonstrations against the shootings broke out in hundreds of college campuses across the United States, McLean may have felt that the students were without leadership, as the "church bells" of the time, possibly the Chicago Seven, involved in leading the anti-war protests during the 1968 Democratic National Convention, were silenced when five were fined and sentenced to prison on February 20, 1970.

The Chicago Seven was a group of militants who opposed the Vietnam War. McLean seemed to believe that when these men were imprisoned that the anti-war movement was without leadership (i.e., without church bells), and would falter. The anti-war movement continued, even though the original leaders were imprisoned. Check this article for more information about the Chicago Seven.

http://en.wikipedia.org/wiki/Chicago_Seven

What exactly are the church bells?

Church bells call people together with one purpose. The Chicago Seven led..they called people together for a cause.

Thank you.