The messianic and eschatological prophecies in chs. 11 & 12 portray a world much like we see in the Revelation of Jesus Christ to the Apostle John. Note, however, that while the world improves dramatically on the one we currently inhabit, it is not entirely perfect. Poverty and wickedness persist as seen in v. 4, and the Messiah will have need of the ability to deal wisely with those problems. It does mention in v. 9 that the sacred mount (Holy Mountain) will be free from anything vile or evil, but that may not apply elsewhere in the world, particularly in the eight other nations mentioned from whence will come redeemed the people of God. These other nations will honor the Messiah and seek His counsel, but the blanket of perfect peace may not extend to these foreign lands.
In fact, v. 14 describes Israel & Judah together plundering those foreign peoples. This in opposition to the standard of nonviolence maintained elsewhere by Isaiah: The prophet describes God taking vengeance on those nations who sin during the fall of Israel and Judah, but warns against his people carrying this out on their own.