Gunnar Myrdal, economist and one of the most prominent Swedish Social Democrats, wrote quite a lot about it. Rika och fattiga länder (Rich and poor countries) in 1957, published in English as Economic theory and underdeveloped regions. Asian Drama: An Inquiry into the Poverty of Nations was published in 1968. He also had pamphlet titled Politiskt manifest om världsfattigdomen, translated into English as The Challenge of World Poverty: A World Anti-Poverty Program in Outline, in 1970. Gunnar and Alva Myrdal have a son named Jan who's written even more, but I wouldn't say he's a Social Democrat (rather much further to the left).