This volume of collected papers takes stock of what has become known about the war in eastern Ukraines Donets Basin (Donbas) between April 2014 and mid-2020. It provides an introduction to the conflict and illustrates the key point of contention in the academic debate surrounding it -- the question whether this war is primarily an internal Ukrainian phenomenon or the result of a covert Russian invasion. The contributions by recognized specialists from Ukraine, Russia, Germany, and Japan offer multifaceted views and insights into this long-lasting conflict for both expert readers and those who are new to the topic. The volumes contributors are Tymofii Brik, Jakob Hauter, Sanshiro Hosaka, Yuriy Matsiyevsky, Nikolay Mitrokhin, Maximilian Kranich, and Ulrich Schneckener.