The King James Version reads that the dragon “went” to make war with the remnant. More recent translations are in agreement that the dragon “went off” (ESV, NASB, NIV, RSV, NRSV) or “went away” (Greek: apelthen) to make war. The KJV reading is based on a relatively rare manuscript option (Greek: elthen) supported by the evidence available at the time when the KJV was produced.
In addition, the manuscript tradition behind the KJV translation has “‘I stood’ upon the sand of the sea” (meaning John: Rev. 13:1, KJV) instead of “‘he stood’ upon the sand of the sea” (Rev 12:18, NRSV; 12:17, ESV, RSV; 13:1), meaning the dragon rather than John. The NIV and NRSV go so far as to translate “dragon” instead of “he” (Rev. 12:18, NRSV; 13:1, NIV). While the manuscript evidence is split fairly evenly on this point, text critics strongly favor “he stood” as the most likely reading in the original.
The readings “went away” and “he stood” fit much better with the story of Revelation 13, where the dragon calls up allies from the sea and the land to assist him in the final conflict. The more modern readings tie chapter 13 with chapter 12 as a continuous narrative. Chapter 13, then, is an explanation of the dragon’s end-time war with the remnant (see present and future tenses in chapter 13). But the dragon’s allies, the beast from the sea and the beast from the earth, both have a history (Rev. 13:1-7, 11) that parallels the middle portion of chapter 12 (Rev. 12:3-6). Thus, chapters 12 and 13 explain each other as part of an ongoing narrative.