BOGOTA—The yellow pages here in the Colombian capital show hundreds of transnational companies. Some are marketing products, some are taking advantage of the country’s varied climates, and others seem to be capitalizing on its minimum wage, about $140 a month. They’ve invested billions of dollars into the Colombian economy and are providing thousands of jobs. But many of the firms don’t seem to protect their employees from attacks in Colombia’s decades-old armed conflict. Last year 184 of the world’s 213 confirmed killings of union members occurred in Colombia, according to the International Confederation of Free Trade Unions. And many of the companies, including at least 17 U.S. military contractors, profit from the war. A look at four transnational firms shows their complex role here.