What kind of alien civilization could be the biggest threat to other civilizations?

What kind of alien civilization could be the biggest threat to other civilizations?

In this writing, I will handle the hypothetical threat, what another civilization can make to its neighbors, and what kind of civilization would-be threat. Sometimes people have discussed, what kind of civilization would be the biggest threat to other civilizations? The offered answer is that the civilization, what has just invented the interstellar traveling and face the primitive race.

That situation would addict that civilization to use force against that neighbor.  When we are thinking that civilization is young and it wants to show how powerful it is to another civilizations and races, the threat would be the civilization, what notices some habitable planet in the solar system, what locates near it, and then that race would send the army to take that planet under control.

But maybe civilization would be wiser or more adult when it starts to create the technology, which makes interstellar traveling possible. When we are thinking about threats, what the other civilization could cause for its neighbors, we can think the situation, that the center star of their solar system would start to grow as a red giant, what means that they must leave their home planet. 

Even if this hypothetical civilization would have the technology to make other planets habitable, and they would create a new home planet in their solar system, or maybe they would transfer the home planet with the growing star. But sooner or later the red giant would end its life, and then the civilization would have to leave or find another energy source.

That could make them so-called grasshopper civilization, what lives in the giant spacecraft, and if their population would grow, that civilization needs materials for making new spacecraft. And that thing could make possible that civilization will turn dangerous. If it comes to the solar system it might destroy the entire planet by shooting it some kind of energy ray, and then benefit entire materials of that planet.

This kind of civilization could act that it would not care about other species, and target the energy ray to planets, where is life forms. Many times in some cosmological writings is mentioned the civilization, what has forced to leave their solar system, but they could not have the possibility or technology to start living in the spacecraft. 

And that species should find the new home planet, and in that case, it might want to conquer the habitable planet. even if there is another intelligent species. That kind of hypothesis consists of the attacks, which are meant for causing harm or even destroy another intelligent species, what that hostile civilization think as the competitor. There is a hypothesis that when some intelligent species lands to the planet, where is primitive civilizations, it starts to play some kind of master race.

If one member of that civilization would be killed, that would cause horrible counter actions. Here we must remember, how human beings have behaved against primitive villains, what have treated the colonialists, who had better weapons. History is full of examples, how "white man" or Europeans and Arabs have acted against villains, what have shot them with arrows.

The responses have been given by artillery and machine guns, and every person of those villains have been killed. But the thing is that when there are two nations, what have similar firepower and equipment against each other, that thing has been caused the respect and willing to discuss even the difficult things.

This thing is visible in the relationships between states, what have nuclear weapons in their arsenals. They would tolerate many things from another nuclear power, but if there would be state, what has less strike capacity than nuclear power and what acts against it, the answer would be the strike against that country. So strike capacity is bringing respect for the nations, and this is the reason, why many new nations are wanted nuclear weapons in their arsenals.