In other words, after Bonhoeffer's time in the U.S. where he was exposed to biblical pacifism, he didn't just modify his views on the state, he had the equivalent of a conversion experience. It transformed the way he looked at everything. It would be the equivalent of an open-carry person suddenly becoming the proponent of massive gun control. Of Saul, the persecutor of Christians becoming Saul, the evangelist.
You read Bonhoeffer's early sermons on national themes, and he endorses the two kingdoms theory. He's all for the defense of national honor. He might not have agreed with Hitler's methods, but he endorsed the underlying reasons for it. But not after his sojourn in the U.S. and his exposure to the Sermon on the Mount in a new way by his French companion...would that more people would encounter the Sermon on the Mount in an unfiltered way!