Albert Barnes Commentary 2 Chronicles 25:10

"Then Amaziah separated them, [to wit], the army that was come to him out of Ephraim, to go home again: wherefore their anger was greatly kindled against Judah, and they returned home in fierce anger." — 2 Chronicles 25:10 (ASV)

Such a dismissal was sure to arouse great indignation. The Israelites would assume they were dismissed because their good faith was suspected. For the consequences of their indignation, see 2 Chronicles 25:13.