Q:

What resources would we fight over in space?

Obligatory Backstory*: In year, whatever the count is now, humans get their black hole ships in working order, and decide to venture into space. We colonize a few worlds, and start establishing some loose connections with other races (think sort of Native American v.s. Europeans, except not necessarily a power difference). Cruising along, we find material X. Material X is very valuable. We see a race, which roughly would be pronounced as numahs in human vocal cords, are hogging it up (numahs are at approximately the same level of development as us, although might use a different system of propulsion). Our military leaders try and negotiate to get some of it, but then they up and decide to slaughter our women and children for no reason besides hating us (and well, the women and children were on the ship that started the battle, but still)! Obviously, numahs don't deserve material X. We will get material X, and they will get none.
End Obligatory Backstory
So humans have always fought over resources, and I don't think we'll stop in space. My question is, what would space faring civilizations fight over? I had a couple ideas, but they don't quite pan out.

Worm Holes: They don't actually exist.
Micro Black Holes: Some what hard to harvest, Doubtful to occur naturally, Not too hard to make
Antimatter: Doubtful to occur naturally, Hard to harvest
Neutron Stars: Hard to harvest, why would you want it
Gold: My favorite so far, Gold could be rare in space too

What other materials could space civilizations fight over. Include both the material, how to harvest it, and why we would fight over it. If you have any reason why the above would be a better idea than I originally thought, feel free to include it.

*Not obligatory for reading, feel free to skip

A:

Fuel sources
Without a fuel source, your spaceship is just drifting space junk. Fuel provides the energy required for life support, movement, and construction. Life support can come from an external power source such as the nearest star but we don't yet have a way to move an object in space without some kind of reaction mass. 
Construction Materials
Building a space empire is going to need lots and lots of construction materials. If building giant ships or space stations is in the plan then finding high grade iron-nickel asteroids will be high on the priority list. (Of course, iron and nickel aren't the only materials you would need.) 
Advantageous Orbital Positions
The Lagrangian points between the earth and moon are very valuable places to be for any number of strategic reasons in relation to a near by planet or sun. 

