This is a question going back to the earliest incarnations of both. I think it's not as simple as just assuming that the Romulans were less warlike because they didn't use bladed weapons and growl and all of that. The more warlike they are on the surface doesn't mean that they are more belligerent. A good analogy is Prussia in the post-Napoleonic 19th century: while known for being a severe military state, they only fought three wars - and all in the span of a decade.
I always thought that Klingons were best when they were evil and incomprehensible from our (future) mindset, while we were natural enemies to them because everything the Federation does is understood by them as aggression. Millions of years of evolving into an advanced warrior race makes them not blink at executing prisoners, taking resources from helpless people, and in summary executions of their own subordinates (and occasionally superiors) if they feel it is justified for the greater good of their own people. They are also fearful of the Federation meddling in their internal affairs and in their expansion - which isn't done with aggressive intent, but it appears to be.
So they're not like children, destroying everything just because they get mad. Being cold and calculating is a strategy to them after all. So while their entire culture is based around martial values, it has more to do with the way that they evolved and because of centuries of necessity.
The Romulans, on the other hand, are almost never portrayed in a very forgiving light. Their whole beginning as a separate race goes back to them choosing to reject a philosophy of peace. Even when they act completely restrained, it is clear that they allow themselves to derive satisfaction from doing all of the same villainous things that Klingons do. It also shows that it is not so much an evolutionary or practical imperative because of their widespread dissent and a need to have armies of secret police to squash it. So it seems to me that the Romulans are, in fact, more militaristic when put in perspective.
I always thought that Klingons were best when they were evil and incomprehensible from our (future) mindset, while we were natural enemies to them because everything the Federation does is understood by them as aggression. Millions of years of evolving into an advanced warrior race makes them not blink at executing prisoners, taking resources from helpless people, and in summary executions of their own subordinates (and occasionally superiors) if they feel it is justified for the greater good of their own people. They are also fearful of the Federation meddling in their internal affairs and in their expansion - which isn't done with aggressive intent, but it appears to be.
So they're not like children, destroying everything just because they get mad. Being cold and calculating is a strategy to them after all. So while their entire culture is based around martial values, it has more to do with the way that they evolved and because of centuries of necessity.
The Romulans, on the other hand, are almost never portrayed in a very forgiving light. Their whole beginning as a separate race goes back to them choosing to reject a philosophy of peace. Even when they act completely restrained, it is clear that they allow themselves to derive satisfaction from doing all of the same villainous things that Klingons do. It also shows that it is not so much an evolutionary or practical imperative because of their widespread dissent and a need to have armies of secret police to squash it. So it seems to me that the Romulans are, in fact, more militaristic when put in perspective.