Interesting I consider belligerence a characteristic related to a rather earlier evolutionary stage than anything... yeah, like cavemen trying to kill each other for land, food, mating and status. In other words, warfare might tell how much a civilization hasn't evolved its technology and social organization so that it still needs to use brute force to supply itself. The more a civilization is evolved, the more they perceive the warfare is nothing but a big waste of energy, resource, time and lives.
A civilization that can make interstellar travels can also generates energy from stars and build atoms straight from thin energy. What can we offer? Water, hydrogen, oxygen, carbon, iron... these things are abundant in the universe, no wonder why these substances are in the top of the periodic table. If something went very bad in their planet it's possible they would have technology to revert, for example, a green-house effect like Venus.
Our poor humanity with a very small number of scientists and researches (while 99% of humanity is wasted in poverty and ignorance) can organize precisely atoms in nano-structures to create super-batteries and circuits so thin as paper. It's because we are just 1% smarter than most animals, now think about what another civilization 1% smarter than us is capable of.
I believe our humanity in the current stage is more threatening than aliens. Our humanity attacking aliens or committing global suicide is more likely than aliens attacking us, even if the later is more powerful than us.
(but, in case of something bad, we have guns... durr derp durr
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