  We solve dynamical equations of motion to determine the conditions under
which an over-dense region in the early universe will lead to collapse to a
black hole, starting from horizon crossing of the over-dense region to the
point of gravitational instability. Here we focus on the sensitivity to QCD and
electroweak phase transitions. We then solve rate equations to determine the
mass distribution of black holes in the present universe. A second order phase
transition or rapid crossover would have significant consequences only if the
index of primordial density fluctuations n > 1.25. However, a first order
transition would lead to a black hole dominated universe for any realistic
value of n including n=1.
