This paper depicts significant events, as well as important doctrines, which affected the traditional comprehension of the terms “international armed conflict” and “non-international armed conflict”, thus showing the process of adapting this distinction from the realm of facts to the realm of law. Although the division between international and non-international armed conflicts is quite old, it was not until the mid-20th century when it was first incorporated in international law. Before the Article 3 common to four Geneva Conventions was established, international law had been dealing only with rights and duties of parts to the international conflicts, regarding non-international conflicts as internal affairs of particular states. Because for many years it had been pointless to seek for norms of international law which generally and abstractly would determine humanitarian standards in case of an outbreak of internal conflict, regulations incorporated in Geneva Conventions of 1949 were first regarded as huge success. Nevertheless, currently they are commonly considered to be too vague and not precise enough. Moreover, they seem to be inadequate to modern armed conflicts – so called “transnational conflicts” or “new wars”, which do not fit in legal frames of “international armed conflict” or “non-international armed conflict”, created over 60 years ago.