Daniel 7:21 (BSB)

As I watched, this horn was waging war against the saints and prevailing against them,

From Daniel 7. Also in the ESV.

Commentary on Daniel 7:21

• John Calvin (Reformed), Calvin's Commentaries on Daniel 7:21: The Prophet now adds what he had omitted. The angel does not yet answer him, but as he had not sufficiently expressed how the little horn waged war with the sons of God, he now supplies the omission. He says, therefore, he saw — this ought to be received by way of correction; I saw, says he, meaning it was shewn me in a vision...
• Matthew Henry (Presbyterian), Matthew Henry's Complete Commentary on Daniel 7:15-28: Here we have, I. The deep impressions which these visions made upon the prophet. God in them put honour upon him, and gave him satisfaction, yet not without a great allay of pain and perplexity (Dan 7:15): I Daniel was grieved in my spirit, in the midst of my body.
• John Gill (Reformed Baptist), Exposition of the Old and New Testaments on Daniel 7:21: I beheld, and the same horn made war with the saints,.... The same little horn before described; not Antiochus Epiphanes, who made war with the Jews, as many think; or the Roman Caesars, that persecuted the church of Christ, as others; nor Titus Vespasian, who fought against Israel, as Saadiah; but antichrist, or the pope of Rome; and this refers to the wars of the...
• Jamieson-Fausset-Brown (Reformed), Commentary Critical and Explanatory on the Whole Bible on Daniel 7:21: made war with the saints--persecuted the Church (Rev 11:7; Rev 13:7). prevailed--but not ultimately. The limit is marked by "until" (Dan 7:22). The little horn continues, without intermission, to persecute up to Christ's second advent (Rev 17:12, Rev 17:14; Rev 19:19-20).