The main theme of Bertolt Brecht's "From A German War Primer" is the relationship between the ruling classes and the working classes. The ruling classes are presented as greedy exploiters of the working classes. The ultimate manifestation of this exploitation is war. The ruling classes send the working classes to fight their wars for them.
At the beginning of the poem, Brecht establishes the grotesque inequality between the ruling classes and the working classes. The ruling classes have "already eaten," while the working classes "must leave this earth / Without having tasted / Any good meat."
Brecht also implies the cynical hypocrisy of the ruling classes, who "TAKE THE MEAT FROM THE TABLE" and at the same time "Teach contentment" to those (the working classes) who go hungry. The ruling classes also "speak to the hungry / Of wonderful times to come," and thus justify or rationalize their hunger with false promises of, and false hope for better times to come.
In the second half of the poem, Brecht focuses on how the ruling classes send the working classes to die in meaningless, ignoble wars. The ruling classes tell the working classes that a war is a "way to glory," whereas in reality it is a way only "to the grave." Brecht also indicates that, on both sides, the "conquerors and conquered," it is always the "common people" who starve.
At the end of the poem, Brecht ominously warns the ruling classes, personified by a "General," that the working classes have the potential, and the real power, to fight back. He reminds the General that, though his tanks and bombers may be "powerful," they need "drivers" and "mechanic(s)" respectively. In other words, the weapons of the ruling classes are powerless without the working classes to drive or fix them. Perhaps another implication is that the working classes, the drivers and the mechanics, will one day turn these weapons against their real enemies—the ruling classes.