Control of centers is determined after every autumn retreat phase. If he moved out of Spain before that time, he would not gain control over it.

@ jwm0112 - you do have to check out the game rules - it just makes no sense to ruin your games otherwise.

And this is a generic rule of Diplomacy - not something specific to this site only?

Here is the statement of the rule directly from version 5 of the official rulebook to Diplomacy by Avalon Hill:
"Once a country gains control of a supply center, it can leave the center vacant and still keep control of it, as long as that center is not occupied by another country at the close of a Fall turn. A unit that moves into a supply center during a Spring turn and moves out of it during the Fall of the same year does not affect the ownership of the supply center. In short, a country retains control of a supply center as long as, at the end of each Fall turn (including retreats), the supply center is either vacant or is occupied by one of its own units."
So what am I (are we) missing?

I don't know... did you read that passage? Let me help:

"A unit that moves into a supply center during a Spring turn and moves out of it during the Fall of the same year does not affect the ownership of the supply center."

umm, could you give us the link? and btw, jwm, if those are your initials, then we have the exact same ones.........just though that was sort of odd.........................

Did you read the sentence after that one, that begins: "In short..."? That seems pretty clear.... When it says "does not affect the ownership" in the preceding sentence, it means by moving out of the supply center ownership is NOT taken away, not the other way around....

Basically if you aren't there in any fall turns to begin with you never had "ownership" to affect. I used to play the way you say, and had a nasty surprise as France with Spain as well lol. But trust me when I tell you that it is correct the way it is.

Here is the link (in pdf - pg 17 of 24):

http://www.wizards.com/avalonhill/rules/diplomacy.pdf

Yeah, everyone else is in agreement jwm, this is just the way it is.

Ownership only changes at the end of each year. I can't make that any more clear. IT does not change party way through and thus, the fact that you were in Spain part way through is meaningless.

@ jwm0112 - France never owned Spain in your scenario. He did not lose it - he never controlled it.

"A unit that moves into a supply center during a Spring turn and moves out of it during the Fall of the same year does not affect the ownership of the supply center."
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I can see how this part may make it a bit confusing. But, if you consider Spain to be neutral, then this sentence applies. It was neutral and stayed neutral.
The next line, however, should clear up any confusion:
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In short, a country retains control of a supply center as long as, at the end of each Fall turn (including retreats), the supply center is either vacant or is occupied by one of its own units.
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In your case, Spain is "owned" by a neutral territory, and it remains neutral because of the above statement.

I understand. Control is not obtained until the territory is held at the end of the Fall turn. Once control is obtained, it is not lost until taken.

Thanks for the help.

Think of it as musical chairs and it only counts what you are sitting on when the music stops.

The other way that I explain things is to think of the Spring move as Tourist Time in Europe where you pass through and take a look at different places, but it is in the Fall that you settle down for the winter and that is the places that count for control.
This is also where we get the term "Spring Raid" to apply to a place that you moved into in the Spring and then moved out without ever establishing control over the province. The most common place for this to occur is Spain in 1901 as the French move through it to get an army in Portugal or
move back to cover Marseilles from a threat via Piedmont or Burgundy and wind up getting back to Marseilles thus again never owning Spain.