From wikipedia
"Neoconservatives are conservatives who are "new" (neo) to the conservative movement in some way. Usually, this comes as a result from the migration from the left of the political spectrum to the right, over the course of many years. Though every such neoconservative has an individual story to tell, there are several key events in recent American history that are often said to have prompted the shift.
Some of today's most famous neocons are from Eastern European Jewish immigrant families, who were frequently on the edge of poverty. The Great Depression radicalized many immigrants, and introduced them to the new and revolutionary ideas of socialism and communism. The Soviet Union's break with Stalinism in the 1950's led to the rise of the so-called New Left in America, which popularized anti-Sovietism along with anti-capitalism. The New Left became very popular among the children of hardline Communist families.
Opposition to the New Left and Détente with the Soviet Union would cause the Neoconservatives to emerge as the first important group of social policy critics from the working class. The original neoconservatives, though not yet using this term, were generally liberals or socialists who strongly supported the Second World War. Multiple strands contributed to their ideas prior to becoming neoconservatives, including the Depression-era ideas of former New Dealers, trade unionists and Trotskyists, particularly those who followed the political ideas of Max Shachtman. The current neoconservative desire to spread democratic capitalism abroad often by force, it is sometimes said, parallels the Trotskyist dream of world socialist revolution. The influence of the Trotskyists perhaps left them with strong anti-Soviet tendencies, especially considering the Great Purges targeting alleged Trotskyists in Soviet Russia. A number of neoconservatives such as Jeane Kirkpatrick, Richard Perle and Paul Wolfowitz were Shachtmanites in their youth while others were involved in the Social Democrats, USA, which was formed by Schachtman's supporters in the 1970s."
more here:
http://en.wikipedia.org/wiki/Neoconservatism_(United_States)#Origins