Germany's a good example. In 1914 the ministry was called Kriegsministerium, and an invasion wasn't seen as a necessarily bad idea. I think it already was, but at the time, you could argue in Berlin that a country that started a war could benefit from that war, if executed well. That kind of argument wouldn't make people doubt your judgment yet.

A few years later it was clear that offense was necessarily a resource loss. Someone who wanted to build a career as a civil servant might then see a defense ministry as a viable option, but not any sort of offensive war. Offense was clearly not viable, and therefore not a good basis for budget allocations, and therefore the good career move for the civil servants was to focus the ministries entirely on defense.