In general, a mournful site of battle (5)
I believe the answer is:
alamo
'battle' is the definition.
(famous mission and siege from the Texas revolution)
'in general a mournful site' is the wordplay.
'in' indicates the answer is hidden within 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" , "1836 massacre at a San Antonio, Texas mission" , "Famous Texan mission" , "US mission" , "Mexicans invested in Texas" .)