Well if they mastered that level of tech they would have also had to mastered actually working together, so they might relatively "peaceful". I mean just think about how much more advanced we would be if we as a species could actually work together.
Just think how much more advanced we would be if we were constantly at war with other States? Or, at least, cold war.
I don't argue that progress can only happen during war, but right now, our best progress is born out of such. The Cold War serves as a key example in recent progress.
But competition in general is what is necessary for progress. Our best hope is peaceful, friendly competition. A world government residing over all the states, removing the anarchistic variable from international politics, would help bring this change to our civilization.
How? The way I see it, if a world government unites everyone under a single banner, states can trade competitively, but not born out of necessity. Multiple parties would be invited to work on the same project, parties that span multiple states and include a large number of participating citizens - be them scientists, engineers, or whatever. This more friendly competition, with large groups working to one solution, would bring not only a great deal of new solutions, but also multiple solutions - solutions that can be used as stepping stones to even greater progress.
And space-traveling species is likely to come across other species. Conflicts will happen due to the nature of sentience.
A species that runs into us, needn't be an aggressor to spell trouble for our way of life. But it could also mean great things to our progress, regardless of the outcome - unless of course it is total annihilation.
If we meet a species that has met other species in war, it could still be a species that has brought united peace to its people. Hell, it could be an extremely peaceful species in general - to be peaceful does not have to equate to being a pacifist, as to uphold peace might require a show of force. Universal politics is something we have no clue over - aggressors could be a very rare thing for all we know, as it could spell trouble for said species in the wide universe. But they arguably exist, as it's simply a product of an anarchistic environment.
For all we know, we may have been monitored for thousands of years, and the united intergalactic body has ordered all species to refrain from contacting our planet. I certainly would - let that miserable planet sort itself out, see if the species can prove themselves fit for their planet as a united species, let alone fit for the stars.
Would
you want to invite us to the Assembly of the Universe, knowing how little we can cooperate with each other? I'd say, let them prove their worth, we'll invite them when they are ready.