Which preposition to use with lancastrians

at Occurrences 2%

Montagu was so encouraged with this success that, while a numerous reinforcement was on its march to join him by orders from Edward, he yet ventured, with his own troops alone, to attack the Lancastrians at Hexham; and he obtained a complete victory over them.

during Occurrences 1%

King Henry V. restored Hotspur's son, the second Earl, to his family honours, and the Percies were staunch Lancastrians during the Wars of the Roses which followed, the third Earl and three of his brothers losing their lives in the cause.

under Occurrences 1%

at the head of the Yorkists completely routed the Lancastrians under the Duke of Somerset.

Which preposition to use with  lancastrians