Uninhabited Aircraft Systems (UAS), as a relatively novel technology, was always seen as a tool available and utilized only by rich and developed states. But thanks to globalizations and the fast proliferation of commercially available drones, this platform has already been used by smaller states and also non-state groups, giving them possibilities never seen before. Yet, there is little research on how and why these new actors use UAS to claim their cause. The research question to guide this thesis is how and why do non-state armed groups differ from states when using Uninhabited Aircraft Systems in their military operations? The thesis uses a demand- and supply-side theory, adapted for the proliferation of drones to help answer that question. This theory is tested in a multiple case study involving the United States as a state and the Houthis as a non-state group during the Yemeni crisis, from 2011 to 2022. Through a structured, focused comparison between the cases, indicators from the demand- and supply-side models were used to understand the differences in drone use between different actors. The main findings are that states and non-state armed groups differ in their use of UAS mainly because they have different boundaries (legal and technological), but also for the symbol and status that this platform carries. Finally, it was seen that the theory is not only able to clarify the trends on proliferation, but also the why actors use UAS, with few remarks, but with a need to test it further.