I think, at least as we saw in 'Enterprise', it's accurate to say that humans were relatively diplomatic. None of the early conflicts between United Earth and anyone else were really Earth's fault, as far as we can tell. The Klingons obviously just distrust humans and think they are weak. The Suliban were being manipulated by another power, same with the Xindi. The Romulans were afraid that Earth could unite the rest of the area's powers (they were right) and become a possible threat to the Empire.
I was basically listing several tendencies that these various species (primarily their governments) have had in the past. I mean, is it not accurate to say that the Romulans' scheming has caused one major war and a few other smaller conflicts? I think that's fair. The Breen are still pretty unknown, but the fact that they have joined up with a larger power to fight the Federation, not once but TWICE, makes me think that they prefer war to diplomacy or negotiation. The Tholians have a history of hostility towards the Federation, but have yet to actually go to war (assuming that doesn't happen later in the Vanguard
series). The Gorn are very territorial from what we have seen, but were basically at peace with the UFP until now (although you can argue that they haven't done anything to jeopardize that yet). So little has been written on the Tzenkethi that it's the hardest of all these species to know what their general relationship with the UFP is. I'm not entirely sure about the Kinshaya, since they have only appeared recently with any frequency in Trek Lit. But it seems like they are not that peaceful.