Earthside:
The first half is about the first half of my main characters story... his history.
The second half is what happens after he leaves and his "friends" are forced to fight off an alien invasion while remaining interconnected with a large political move, on the brink of a second world war (I say second because these wars are much larger than our previous world wars).

Dimension:
The first... oh I'd say the first sixth of this story is an introduction to what happens before my main character arrives, while the latter five sixths are a war story, where this character is only mildly important.

If I put them TOGETHER, though, it would create a lot of time gaps in between the main char's history. That's bad.
On the other hand (aside from five different fingers) this would give me a good "bounce back" storyline to go in between the plots on Earth and the story elsewhere.