We prove an analogue of Klein combination theorem for Anosov subgroups by using a localto-global principle for Morse quasigeodesics. arXiv:1805.07374v2 [math.GR] 4 Jul 2018 free products and HNN extensions. These so called "Klein-Maskit combination theorems" have been generalized to the geometrically finite subgroups of the isometry groups of higher dimensional hyperbolic spaces by several mathematicians. For instance, in [BC08], Baker and Cooper proved the following theorem.Theorem 1.1 (Virtual amalgam theorem, [BC08]). If Γ 1 and Γ 2 are two geometrically finite subgroups of Isom (H n ) which have compatible parabolic subgroups, and if H = Γ 1 ∩Γ 2 is separable in Γ 1 and Γ 2 , then there exists finite index subgroups Γ 1 and Γ 2 of Γ 1 and Γ 2 , respectively, containing H such that the group Γ 1 , Γ 2 generated by Γ 1 and Γ 2 is geometrically finite, and is naturally isomorphic to the amalgam Γ 1 * H Γ 2 .When Γ 1 and Γ 2 intersect trivially, the "compatibility condition" in the above theorem simply means that the limit sets of Γ 1 and Γ 2 in ∂ ∞ H n are disjoint. Since this case would be most relevant to our work, we state it separately.Corollary 1.2. If Γ 1 and Γ 2 are two geometrically finite subgroups of Isom (H n ) with disjoint limit sets in ∂ ∞ H n , then there exists finite index subgroups Γ 1 and Γ 2 of Γ 1 and Γ 2 , respectively, such that the group Γ 1 , Γ 2 generated by Γ 1 and Γ 2 is geometrically finite and is naturally isomorphicThere are also certain generalizations of these combination theorems in the realm of subgroups of hyperbolic groups and, more generally, isometry groups of Gromov-hyperbolic spaces. In [Git99], Gitik proved that under certain conditions two quasiconvex subgroups of a δ-hyperbolic group "can be virtually amalgamated." In this regard, our main theorem is an analogue of [Git99, Corollary 3]. See also the papers by Martínez-Pedroza [MP09] and Martínez-Pedroza-Sisto [MPS12] for closely related results.In the present work, we prove a combination theorem for Anosov subgroups of semisimple Lie groups. Anosov representations of surface groups (and, more generally, fundamental groups of compact negatively curved manifolds) were introduced by Labourie [Lab06] to study the "Hitchin component" of the space of reducible representations in P SL(n, R). Guichard and Weinhard [GW12] generalized this notion in the setting of representations of hyperbolic groups in real semisimple Lie groups. Anosov subgroups can be regarded as higher rank generalizations of convex-cocompact subgroups of isometry groups of negatively curved symmetric spaces.Our main result presents an analogue of Corollary 1.2 for Anosov subgroups. Before stating our theorem, we briefly discuss our framework. Let G be a semisimple Lie group, let P be a maximal parabolic subgroup conjugate to its opposite subgroups.Our main result is the following.