The 1991 Persian Gulf War, involving more than a half million U.S. troops, was the largest U.S. military action since the Vietnam War, and the largest ever in that part of the world. But it was not the first time the U.S. had become militarily involved in the Persian Gulf, and it might not be the last. The interests that motivated the U.S. to wage war in 1991 remain, and could possibly spur future U.S. military involvement in the region.

Oil was and is a primary motivation for U.S. involvement in the Persian Gulf. Oil is a vital part of the U.S. economy, accounting for 43 percent of U.S. energy use. In 1990 the U.S. imported half the oil it consumed, with much of this oil coming from nations ringing the Persian Gulf. The eight countries in the region—Iraq, Iran, Saudi...