  We prove that the fundamental group of a finite graph of convergence groups
with parabolic edge groups is a convergence group. Using this result, under
some mild assumptions, we prove combination theorems for a graph of convergence
groups with dynamically quasi-convex edge groups (Theorems 1.3, 1.5). In the
proofs of these results, we are generalizing Dahmani's technique. Finally, we
prove that the fundamental group of a graph of relatively hyperbolic groups
with edge groups either parabolic or infinite cyclic is relatively hyperbolic
and construct the Bowditch boundary.
