Earth defense force/starship troopers based.
The galactic alliance, about the same time humans came in the alliance (but long enough for the alliance to realize humans' nature), is at war with a unintelligent but somehow space traveling insect race and are slowly losing. The alliance asks the humans for help to defeat them, asking for ships, attack vehicles, weapons, and soldiers. The humans misunderstand what they meant and take it as "Our equipment can only hold them, we need you humans to push them back". -- Anon Guest
For the longest time, the Galactic Alliance thought that the Human Motto was Make love and war. No efforts to correct them on this assumption proved efficacious. After all, Humans were both persistent and good at both of them, as evidenced by numerous close and even closer encounters before the Alliance finally welcomed Humans into their club.
The mistake they made was in underestimating just how much practice Humans had had at war. When the swarming Acridith threatened, and the Alliance fleet had to hold them back from their expanded and expanding territories, they asked the Humans to help. Specifically, "help push them back." They expected the status quo, where the new allies re-established the neutral zone and thinned the population to the point where the Acridith could live well for another century or so. Thing is... Humans don't think like that.
Humans have been at war since one tribe thought another tribe was looking at them funny. When ideologies weren't enough, they declared war on concepts. When concepts weren't enough, they declared war on actions. When actions weren't enough... well. They'd found other civilisations by then, and their trigger fingers always itched. They dived into war like ducks into water. It was, after all, their element.