In this paper, we propose a novel wireless scheme that integrates satellite, airborne, and terrestrial networks aiming to support ground users. More specifically, we study the enhancement of the achievable users' throughput assisted with terrestrial base stations, high-altitude platforms (HAPs), and satellite stations. The goal is to optimize the resource allocations and the HAPs' locations in order to maximize the users' throughput. In this context, we formulate and solve an optimization problem in two stages: a short-term stage and a long-term stage. In the short-term stage, we start by proposing an approximated solution and a low complexity solution to solve the associations and power allocations. In the approximated solution, we formulate and solve a binary linear optimization problem to find the best associations and then we use the Taylor expansion approximation to optimally determine the power allocations. In the latter solution, we propose a low complexity approach based on a frequency partitioning technique to solve the associations and power allocations. On the other hand, in the long-term stage, we optimize the locations of the HAPs by proposing an efficient algorithm based on a recursive shrink-and-realign process. Finally, selected numerical results underline the advantages provided by our proposed optimization scheme.