We prove a combination theorem for trees of (strongly) relatively hyperbolic spaces and finite graphs of (strongly) relatively hyperbolic groups. This gives a geometric extension of Bestvina and Feighn’s Combination Theorem for hyperbolic groups and answers a question of Swarup. We also prove a converse to the main Combination Theorem.
"A combination theorem for strong relative hyperbolicity." Geom. Topol. 12 (3) 1777 - 1798, 2008. https://doi.org/10.2140/gt.2008.12.1777