Matthew Henry Presbyterian @wholebiblehenry

Here is a short account of the short and inglorious reign of Amon, the son of Manasseh. Whether Manasseh, in his blind and brutish zeal for his idols, had sacrificed his other sons - or whether, having been dedicated to his idols, they were refused by the people - so it was that his successor was a son not born till he was forty-five years old.

Commenting on 2 Kings 21:19-26

John Gill Reformed Baptist @doctorgill

And the servants of Amon conspired against him,.... Some of his domestic servants, and perhaps his courtiers, not on account of his idolatry, but for some ill usage of them: and slew the king in his own house: which they had an opportunity to do, being his servants.

Adam Clarke Methodist @methodicalclarke

The servants of Amon conspired - What their reason was for slaying their king we cannot tell. It does not seem to have been a popular act, for the people of the land rose up and slew the regicides. We hear enough of this man when we hear that he was as bad as his father was in the beginning of his reign, but did not copy his father's repentance.