What would they run out of? You can synthesize elements if you care to expend the energy, and use less than any theoretical form of star travel imaginable. Recycling has got to be cheaper than going to another star system.
Beings with different beliefs will have quarrels. If those quarrels don't lead to understanding they will lead to conflict. Sometimes even understanding leads to conflict.
Whatever is the point here? People quarreling are not a war. Wars are government actions. Individual psychology is not relevant to government, editorial cartoons representing nations as individuals notwithstanding.
I really don't understand why you think cheap star travel denigrates the need to import resources? Does the only form of star travel you think is possible have a by product of limitless energy and resources? Cheap star travel (as with all forms of cheap transportation) makes importing resources that much more viable.
Answer to first question: I don't think there will be a really cheap form of star travel, cheap meaning doesn't require a lot of resources. That's for moronic, low grade scifi like Lost in Space and BattleStar Galactica. But if resources become so abundant, i.e., cheap, that even something as extravagant of resources like star travel becomes cheap, then, naturally, with such abundant resources,
there's no need to go get more.
Answer to second question (I think, there's a typo in there.): Yes, as a matter of fact, I do think that any conceivable form of star travel is going to be astronomically proligate of energy. Either it must involve monkeying around with space time or it follows special relativity. In the first case, we know how much energy it takes to warp space. The Earth only warps space enough to produce a 9.8 meter per second squared acceleration! The energy equivalent is given by the famous equation E equals m c squared. The c squared is equal to 9X10E16 kilogram-meters squared per seconds squared.
times the mass of the Earth. People often don't know there are currently theoretical "ways" to have a star ship, but these are all practical impossibilities.
Special relativity of course tells us that as a mass is accelerated, it's mass increases, meaning it takes more and more fuel. To actually reach the speed of light means an infinite amount of fuel. Given that most of the fuel goes to accelerating the fuel tanks, the payload is going to be somewhat light. That takes a lot of gas.
I always assume that the spaceships, however they're supposed to be traveling from place to place in warp or hyperdrive or whatever the double talk is, are going more or less low speeds. Indeed I don't think of them as being accelerated at all. When it's suggested otherwise, like the "breaking the back" of the Galactica, I just laugh at the stupidity.
There are two problems at the root of all this nonsense. One is not grasping the difficulty of star travel (which will probably never happen.) I can't really give an entire education in basic science on the internet.
The other is the unfounded certainty that war is inevitable, just because. The relative lack of war in South American history, or the long periods of peace in Europe, alone show that this is not a reasoned position. It's just stupid, evil apologetics.