Neoconservatism has a complex parentage, partly home grown and even more European. It originally grew out of tensions internal to many liberals who made up a crucial part of the Democratic coalition Franklin Roosevelt had created, a coalition that had long maintained Democratic political supremacy. This alliance was dominated by managerial liberals, but some focused more on domestic policies, others more on foreign policy. Future Neoconservatives were distinguished by their emphasis on waging an aggressive anti-communist foreign policy after WWII. They were among those called “Cold War Democrats.”
The 60s challenged the complacent New Deal hegemony within the Democratic Party, which then began to fragment. In particular, some became convinced the war in Vietnam was a mistake while others remained convinced winning it was crucial to defeating Communism. Future Neoconservatives were in this second group.
Other developments exacerbated these tensions. Liberalism’s ideal had always been color blind, and some liberals had provided the core of white support for civil rights. But growing militancy in the Black community and the failure of public policies such as Urban Renewal led to widespread questioning of how best to achieve racial equality. Mandatory bussing of school children led to increased white flight while the debate over Affirmative Action convinced many liberals Lyndon Johnson’s Great Society had been guilty of utopian overreach, especially on racial issues. In response, other liberals emphasized Medicare’s considerable successes in improving health care and expanded Social Security in ending poverty among the elderly. The record of Democratic liberal successes and failures was mixed, providing powerful examples to both approaches.
Some New Deal liberals maintained a chastened but still firm belief that good public policy could improve Americans’ lives, others became increasingly skeptical that any such outcomes could be expected. On balance the programs that succeeded received little attention while the failures generated book after book. Future Neoconservatives were often authors of those books.
Finally, future Neoconservatives were appalled at the campus protest movements and alarmed at the cultural “decay” they identified with the counter culture. Feminism in particular was seen as subversive of good order at home and manly preparedness abroad. By lumping all the youthful political and cultural movements of the 60s into a single pot, and labeling it bad, those most alarmed began to question liberalism’s traditional concern with individual rights and liberties.
As the 60s passed into the 70s the intensity of these differences with other Democratic Party liberals grew, and many Neoconservatives began shifting to a more politically ambiguous self-definition. The term “Neoconservative” had initially been a term of criticism coined by the left as some of their more moderate colleagues moved right.
Some, but by no means all, future Neoconservatives had initially become liberals through disillusionment with various Marxist groups with whom they had flirted while young. For Neoconservatives, such as Irving Kristol, their anti-communism was personal, sincere, and deeply rooted. By contrast, their liberalism was derivative, having been acquired in reaction to leftist excesses and tyranny rather than from a personal commitment to its principles. Their liberalism was more a matter of convenience rather than principle, and as easily jettisoned in their old age as they had once rejected it when young.
In time those described as Neoconservative embraced the name. With Ronald Reagan’s presidency, many Neoconservatives began entering Republican ranks, attracted by his antagonism to feminism and the 60s as well as his emphasis on anti-communism. With Communism’s collapse their attention turned towards redefining American foreign policy as well as continuing their cultural jihad against the 60s.
The second generation of Neoconservatives completed the migration, and includes an impressive number of offspring descended from the first. Bill Kristol is the elder Kristol’s son. John Podhoretz is the son of Norman Podhoretz. Frederick and Robert Kagan are the sons of Donald Kagan, another leading first generation Neoconservative. Not all Neoconservatives share this familial heritage, but leading ones disproportionately do.  By the time they completed this transition to a new generation they had completed their departure from American liberal traditions to embrace European attacks on them.
 A good discussion focusing on academics who became Neoconservatives is in Anne Norton, Leo Strauss and the Politics of American Empire, (New Haven: Yale University Press 2004), 44-55.
 Drury explores this point in depth regarding Irving Kristol. See Drury, 137-62.
 A good overview of this transformation is in E. J. Dionne, jr., Why Americans Hate Politics, (NY: Touchstone, 1992) 55-76.
 For a history of those Neoconservatives with Marxist roots to their importance today, see Jacob Heilbrunn, They Knew They Were Right: The Rise of the Neocons, (NY: Doubleday, 2008).