WCF 23.2.
It is lawful for Christians to accept and execute the office of a magistrate, when called thereunto: (Prov. 8:15–16, Rom. 13:1–2, 4) in the managing whereof, as they ought especially to maintain piety, justice, and peace, according to the wholesome laws of each commonwealth; (Ps. 2:10–12, 1 Tim. 2:2, Ps. 82:3–4, 2 Sam. 23:3, 1 Pet. 2:13) so, for that end, they may lawfully, now under the new testament, wage war, upon just and necessary occasion. (Luke 3:14, Rom. 13:4, Matt. 8:9–10, Acts 10:1–2, Rev. 17:14, 16)