Situations of hostility between States and armed groups located on the territories of other States are difficult to classify because they call into question the categories of international and non-international armed conflicts. This contribution argues for the single classification of non-international armed conflicts of those transnational armed conflicts. The article starts with a clarification on the relevant circumstances for the contribution. The different classifications proposed by scholars, tribunals and States are then examined, leading us to our arguments for a single classification of non-international armed conflicts, and to the test adopted for a rapid categorization of those transnational hostilities. Finally, we mention some important observations and challenges on this topic, like the classification of situations involving at the same time hostilities between a State and an armed group located on the territory of another State and the occupation of the territory of this second State.