If by “previous marines” you mean the news report at the beginning of the movie?
That’s the invasion of Klendathu that Rico goes on after BA gets hit. We even see the reporter giving the report from a different angle later in the movie.
Ah. Presumably these were lost in some other conflict, probably against other humans. We don’t know of any OTHER Aliens, and since the war hasn’t started yet we don’t know one way or another.
If by “previous marines” you mean the news report at the beginning of the movie?
That’s the invasion of Klendathu that Rico goes on after BA gets hit. We even see the reporter giving the report from a different angle later in the movie.
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Ah. Presumably these were lost in some other conflict, probably against other humans. We don’t know of any OTHER Aliens, and since the war hasn’t started yet we don’t know one way or another.