If good fences make good neighbors, then the world is experiencing an unprecedented outbreak of neighborliness. The latest country to start building a wall - a "security fence" - is Thailand, to stop terrorists from crossing into Thailand's restive Muslim-majority southern provinces from northern Malaysia. India's 3,000-km. barrier along its border with Pakistan is largely complete, and India is now building a 3,300 km. barrier to halt illegal immigration from Bangladesh. China is now building a fence along its frontier with North Korea as a precautionary measure to stop an immense wave of refugees if the regime in Pyongyang collapses. Pakistan is building a 1,500-mile fence with Afghanistan, Uzbekistan has built a fence along its border with Tajikistan, the United Arab Emirates is erecting a barrier along its frontier with Oman, and Kuwait is upgrading its existing 215-km. wall along the Iraqi frontier. Saudi Arabia has been quietly pursuing an $8.5 billion project to fence off its porous border with Yemen, but the highest priority now is to get a high-tech barrier built along the 900-km. border with Iraq.