The article examines the exact conditions for classifying an armed conflict under international humanitarian law against the backdrop of the crisis in Ukraine, taking into account the difficult factual situation on the ground and the involvement of the different parties to the conflict. Apart from dealing with the requirements of an international or a non-international armed conflict, it looks again into the specific circumstances for the “internationalization” of an internal armed conflict. In doing so, the author revisits the various approaches found in the jurisprudence of the International Court of Justice in its 1986 Nicaragua and 2007 Genocide judgments, as well as in the 1999 ICTY Tadić appeals judgment. Using the attribution regime of the Articles on State Responsibility, he then suggests a solution for determining the degree of control an outside State needs to have over the insurgent party of a non-international armed conflict in order to turn into an international one