Thomas Mann's quote about war and the cowardice that is intrinsic to it is a reflection of his own experience. His relationship to war is one in which there is a repudiation of its supposed benefits. As a boy, he grew tired of military school. As a writer, he pledged his loyalty to the artist being aligned to the life of free creation and not bound to the nationalist machinery of war. Mann's life as a thinker is one in which modernity is seen as a complex and intricate notion, something that war denies with its simplistic and binary understanding.
In the quote, these beliefs are evident. For Mann, peace is a complex state of being. It requires the freedom and courage to look at life for what it is, to stare at it and understand that complexity in allowing different voices is the price of modernity. War's singular focus and reductive condition into arbitrary "friends" and "foes" evades this. In war, there is a simplicity. The soldier kills in name of country. "So and so" is bad and "so and so" is good." War silences voices of dissent and empowers those in the position of power. These are simplistic formulas that enable individuals to remove the complexity that is a part of peace. There is an awkwardness present in the need to listen to another point of view, to seek compromise, and to establish a realm of being where individuals who are fundamentally different both share in an equal claim to consciousness. The problems of this condition requires an individual to possess the courage to understand "the other," as opposed to obliterating it. In this, one sees how Mann's quote of the cowardice of war as a response to the complex problems of peace is evident.