Mother Courage, at its core, is a modernist play. The play fiddles with conventions, using avant-garde techniques to subvert the audience’s expectations and create something new. In addition to being modernist, the play has a strong anti-war and anti-capitalist bend, thereby placing itself in the Marxist tradition.
Furthermore, the play is an example of what Brecht called “Epic Theater,” a type of drama meant to discourage the audience from empathizing with the characters in a play so that viewers can judge the message of the play itself more objectively. Brecht believed that this more dispassionate consideration of a drama’s arguments would be more inclined to produce genuine social change than plays that focus on total immersion.
There is also a case for Mother Courage to be read as a tragedy. In classical tragedies, virtuous heroes are driven to their own ruin by a fatal flaw. Similarly, in Mother Courage, most of the characters are driven to ruin by their own "flaw." Eilif destroys himself with his martial brutality, Swiss Cheese gets executed due to his honesty (that is, his decision to hide the Protestant army’s cashbox instead of pocketing what’s inside), Kattrin sacrifices her life out of selfless love, and Mother Courage contributes to destruction through her callous obsession with profit.