Since they copied it directly from previous works, and it is a term currently in use in various places, can they actually trademark it?
No. Trademarks are not like copyright - there is a formal approval process, though "first use in commerce" also counts somewhat. Games Workshop was granted a 1987 trademark on the term "space marine" in "board games, parlor games, war games, hobby games, toy models and miniatures of buildings, scenery, figures, automobiles, vehicles, planes, trains and card games and paint, sold therewith." They have a second trademark for "video computer games; computer software for playing games".
This trademark is suspect, but it's now law. However, they have no protection for, say, novels or ebooks. Which makes their takedown pure bullying.
USPTO data below.
Word Mark SPACE MARINE
Goods and Services IC 028. US 022. G & S: board games, parlor games, war games, hobby games, toy models and miniatures of buildings, scenery, figures, automobiles, vehicles, planes, trains and card games and paint, sold therewith. FIRST USE: 19870900. FIRST USE IN COMMERCE: 19871000
Mark Drawing Code (1) TYPED DRAWING
Serial Number 74186534
Filing Date July 19, 1991
Current Basis 1A
Original Filing Basis 1A
Published for Opposition November 23, 1993
Registration Number 1922180
Registration Date September 26, 1995
Owner (REGISTRANT) GAMES WORKSHOP LIMITED CORPORATION UNITED KINGDOM Willow Road, Lenton Eastwood Nottingham NG7 2W5 UNITED KINGDOM
Attorney of Record Naresh Kilaru
Type of Mark TRADEMARK
Register PRINCIPAL
Affidavit Text SECT 15. SECT 8 (6-YR). SECTION 8(10-YR) 20051125.
Renewal 1ST RENEWAL 20051125
Live/Dead Indicator LIVE
Word Mark SPACE MARINE
Goods and Services (CANCELLED) IC 002. US 006 011 016. G & S: [paints, namely, water based acrylic paints for artists]
IC 009. US 021 023 026 036 038. G & S: video computer games; computer software for playing games
Mark Drawing Code (1) TYPED DRAWING
Serial Number 75010236
Filing Date October 25, 1995
Current Basis 44E
Original Filing Basis 44D
Published for Opposition July 8, 1997
Change In Registration CHANGE IN REGISTRATION HAS OCCURRED
Registration Number 2100767
Registration Date September 30, 1997
Owner (REGISTRANT) Games Workshops Limited CORPORATION UNITED KINGDOM WILLOW ROAD LENTON, NOTTINGHAM UNITED KINGDOM NG72 2WS
Attorney of Record Naresh Kilaru
Priority Date September 20, 1995
Prior Registrations 1922180
Type of Mark TRADEMARK
Register PRINCIPAL
Affidavit Text SECT 15. PARTIAL SECT 8 (6-YR). SECTION 8(10-YR) 20080422.
Renewal 1ST RENEWAL 20080422
Live/Dead Indicator LIVE