The Cold War ended in 1991, yet the North Atlantic Treaty Organization still persists. This outcome defies paradoxically two exceedingly important facts: First, NATO’s central and greatest geostrategic rival—the Soviet Union—disappeared a quarter of a century ago. Second, China and Russia are insufficiently capable to individually challenge and counterbalance NATO’s military supremacy and conventional military might. From a theoretical perspective, in the absence of an immediate threat and/or the need to counterbalance relative power, International Relations alliance theory would posit the dissolution of military alliances. Nonetheless, NATO continues to endure. This study seeks to elucidate the strategic factors generating this puzzling historical and theoretical development. This study demonstrated that the political economy of the defense industry has become an important variable that can affect the power of states and the endurance of alliances. The study analyzed three equivalent cases of military alliance dynamics—the aftermath of the Great World War, the Second World War, and the post-Cold-War phase of NATO. The analysis of these three cases served to probe and demonstrate the necessary and sufficient conditions for the presence and endurance of military alliances. According to International Relations alliance theory such conditions should be, first, the presence of external threats and, second, the compatibility of national interests. This study employed the comparative case study method in order to shed light on the nature of threats faced by great powers during different time periods. Further, the study used the focused comparison method in conjunction with the intensive case study approach to explore in depth the states’ strategic military and economic interests and alliance decisions. Having analyzed the external threats and compatibility of great power interests in different time periods, the study concluded that neither of the two abovementioned conditions is sufficient to explain the endurance and deepening of the level of cooperation among the great powers participating in NATO. This study demonstrated that technological features of military production—the size and extent of scale economies, economies of scope, and learning-by-doing—and escalating military costs have been crucial and complementary factors affecting the motivations and intra-alliance politics of NATO member-states after the Cold War.