Understanding collective properties of driven particle systems is significant
for naturally occurring aggregates and because the knowledge gained can be used
as building blocks for the design of artificial ones. We model self propelling
biological or artificial individuals interacting through pairwise attractive
and repulsive forces. For the first time, we are able to predict stability and
morphology of organization starting from the shape of the two-body interaction.
We present a coherent theory, based on fundamental statistical mechanics, for
all possible phases of collective motion.