I would react like the rest of society. We all would. We would likely assume inferiority and humble ourselves into submission. Mankind has frequently been faced by the challenge of being confronted by foreign people. At one point, it was the tribe on the other side of the river, then the tribe across the mountain range, then the society across the sea. Any civilization across space would be no different. However, those were other people--familiar to us, at least relatively. Humans assume superiority over other humans. However, as any sort of literature, art, or popular culture indicates, humans are scared of unknown beings. Aliens are always depicted as being more powerful and more intelligent. We would try to make peace; not in the name of peace, but in the name of fear. If the aliens had no interest in peace, but in domination, we would no longer humble ourselves. We would fight.