CROWDS AND RIOTSthe final set of participants relevant to most in-
stances of crowd behavior. Since they are the
guardians of public order, their primary aim with
respect to crowds is to maintain that order by
controlling crowd behavior both spatially and tem-
porally or by suppressing its occurrence. Given
this aim, social control agents can clearly have a
significant impact on the course and character of
crowd behavior. This is evident in most protest
demonstrations and victory celebrations, but it is
particularly clear in the case of riots, which are
often triggered by overzealous police activity and
often involve considerable interpersonal violence
perpetrated by the police. The urban riots of the
1960s in the United States illustrate both tenden-
cies: police-citizen scuffles occasioned by traffic
citation encounters or arrests sometimes func-
tioned as a triggering event (Kerner 1968); and the
vast majority of riot-associated deaths were attrib-
uted to social control agents (Bergesen 1980; Kerner
1968). This was not the case, however, with the
riots in Miami in 1980 and in South Central Los
Angeles in 1992, in which the clear majority of
deaths were at the hands of civilians (McPhail
1994; Porter and Dunn 1984). Although these
different sets of findings caution against prema-
ture generalization regarding the attribution of
responsibility for riot-related deaths, they do not
belie the important role of social control agents in
affecting the course and character of crowd epi-
sodes (Della Porta and Reiter 1998).
Although there is no consensual taxonomy of
crowd behaviors and interacting participation units,
the foregoing observations indicate that behavior-
al and participant heterogeneity are characteristic
features of most crowd episodes. In turn, the
research on which these observations are based
lays to rest the traditional image of crowds as
monolithic entities composed of like-minded peo-
ple engaged in undifferentiated behavior.
CONDITIONS OF EMERGENCEUnder what conditions do individuals come to-
gether collectively to engage in crowd task activi-
ties constitutive of protest or celebration, and why
do these occurrences sometimes turn violent or
riotous? Three sets of interacting conditions are
discernible in the literature: (1) conditions of
conduciveness; (2) precipitating ambiguities or
grievances; and (3) conditions for mobilization.
Conditions of Conduciveness. The concept
of conduciveness directs attention to structural
and cultural factors that make crowd behavior
physically and socially possible (Smelser 1963).
Conditions of conduciveness constitute the raw
material for crowd behavior and include three sets
of factors: ecological, technological, and social
control. Ecological factors affect the arrangement
and distribution of people in space so as to facili-
tate interaction and communication. One such
factor found to be particularly conducive is the
existence of large, spatially concentrated popula-
tions. The vast majority of campus protest demon-
strations in the 1960s occurred on large universi-
ties, for example. Similarly, the urban riots of the
1960s typically occurred in densely populated resi-
dential areas, where there were large, easily mobi-
lizable black populations. Seymour Spilerman’s
(1976) aggregate-level research on the occurrence
of these riots found an almost linear relationship
between the size of a city’s black population and
the likelihood and number of disorders experi-
enced, thus suggesting that there was a threshold
population size below which riots were unlikely.
More recent analyses of the 1960 riots have found
that ‘‘the propensity to riot was a function of far
more than simply the number of Blacks available
for rioting in a particular city’’ (Myers 1997, p. 108;
Olzak, Shanahan, and McEneaney 1996), but such
findings do not suggest that concentrated popula-
tion density and the prospect of rioting are unre-
lated. Thus, these findings, in conjunction with the
earlier observations, provide support for the hy-
pothesis that, all other things being equal, the
greater the population density, the greater the
probability of crowd behavior.The heightened prospect of interpersonal in-
teraction and communication associated with popu-
lation concentration can also be facilitated by the
diffusion of communication technology, namely
telephone, radio, television, and Internet access.
But neither the diffusion of such technology nor
population density guarantee the emergence of
crowd behavior in the absence of a system of social
control that allows for freedom of assembly and
speech. It has been found repeatedly that inci-
dence of public protest against the state diminish-
es considerably in political systems that prohibit
and deal harshly with such crowd behavior, where-
as the development of a more permissive attitude