  We state and prove a combination theorem for relatively hyperbolic groups
seen as geometrically finite convergence groups. For that, we explain how to
contruct a boundary for a group that is an acylindrical amalgamation of
relatively hyperbolic groups over a fully quasi-convex subgroup. We apply our
result to Sela's theory on limit groups and prove their relative hyperbolicity.
We also get a proof of the Howson property for limit groups.
