In general, a mournful site of battle (5)
I believe the answer is:
Here is my best explanation:
'battle' is the definition.
(famous mission and siege from the Texas revolution)
'in general a mournful site' is the subsidiary indication.
'in' says the answer is hidden in the clue.
'alamo' is hidden within 'general a mournful site'.
'of' is the link.
(Other definitions for alamo that I've seen before include "Fort in San Antonio, once famously besieged", "Where Davy Crockett met his end", "Where Jim Bowie died", "San Antonio mission", "Massacre scene in Texas", "Site of a Texas siege, 1836", "Site of 1836 massacre in Texas", "The --, Texan mission besieged in 1836", "Famous mission in Texas" and "Mission building in Texas, site of famous siege by Mexico".)