A less appreciated factor pushing assimilation [of immigrants] was the American legal system, which compelled people to adopt American marriage and inheritance practices. However attached immigrants may have been to their own practices, if they were incompatible with our family culture, they could not maintain them here for more than a generation or two. Other cultural systems could not take root or survive for long in America because the law would not enforce any other system with regard to spouse selection, inheritance, or household formation.One of the central themes of Lotus and Bennett's book is that America's characteristic individualism is baked into the structure of the American family, which has been from its beginning an "absolute nuclear family" type. In such a family system, the "family unit" is understood to mean a mother, father, and their under-aged children. Unlike, say, in premodern China, where sons would live with their parents until their parents' death and (and a daughter would move into her husband's household, living under the subjection of her in-laws), in the Anglosphere there is the expectation that a married couple would go off and establish their own independent household. Along with this conception of the family comes a certain set of norms (such as "individuals freely select their own spouses," "there are no limitations on whom a person can marry, except that marriage to close relative is forbidden," "women enjoy a high degree of autonomy compared to most cultures," and "extended families are weak").  These norms are centuries old, preceding the colonization of America itself.
The protection of choice in marriage partners, especially for women, was critical to the assimilation process. People who moved to America, and more importantly their children, faced no legal obstacles, and few social ones, to choosing their own spouses. In America, parents had no legal authority to interfere with the marriage decisions of adult children, whatever the law and customs may have been back in the "old country." The children of immigrants often wanted to marry someone from outside their ethnic or religious community. They then necessarily formed their own families outside of one or the other other cultural milieu they came from, or outside of both.
The story of immigrants coming to America for opportunity and freedom, but feeling they are losing their children to a culture they do not always like or understand, is an old one that been repeated many times. There is an element of sadness to this. This process of loss of the old way of may be be felt as tragic by the parents but it has been a triumph for Americans over the centuries. We have peacefully, though not painlessly, assimilated millions of people one marriage and one family at a time, into a shared culture. 
Lotus and Bennett slightly exaggerate the continuity of the American family type. There has been significant variation in household size and type over the course of American history, and in the early periods there was significant geographic variation as well.  Of the four central settler cultures identified by David Hackett Fisher, only one—the Puritans—lived and married according to type. The Cavaliers did not frown on cousin marriages, and the Scots-Irish were devoted clansmen; both Cavalier and Scots-Irish patriarchs made it a custom to decide who their daughter would and would not marry, while the Quakers went even further, giving not only parents, but extended family, church leaders, and even neighbors a veto on the marriage choices of their children. 
It is interesting to see, however, how quickly many of these practices died out. By end of century Quaker church courts are filled to the brim with young colonists who have violated one of their community's gravest rules: do not marry outside of the Church.  Custom might keep Cavalier fathers and Quaker neighbors interfering in other's marriage beds, but it seems that the English common law gave them no legal right to do so. As water flows to the lowest point, so any society whose legal regime protects a woman's free choice will inevitably settle into a society of love-marriages. Thus while there was still some variation in practice at different parts of the social strata, the ideal of the freely chosen love-match was firmly enshrined in all regions of the country by 1820.  So it has been ever since.
This puts a new spin on Karl Marx's famous description of industrialization's effect on tradition and sense of place:
All fixed, fast-frozen relations, with their train of ancient and venerable prejudices and opinions, are swept away, all new-formed ones become antiquated before they can ossify.It is a poetic passage. But in the American case it is not even half the story. Ask those in a conservative immigrant subculture why "all that is solid melt[ed] into air" after they moved to this country, and they will tell you the truth: nothing has tore their world apart quite like the centuries old English marriage system.
To read the first post in this series, see Against Patrick Deneen (I). For past writing on the relationship between family structure and individualism, read Historians, Fear Not the Psychologists and Taking Cross Cultural Psychology Seriously. The post "Conservatism's Generational Civil War" provides some of the additional context for what I am doing here. To get updates on new posts published at the Scholar's Stage, you can join the Scholar's Stage mailing list, follow my twitter feed, or support my writing through Patreon. Your support makes this blog possible.
 Michael Lotus and James Bennett, America 3.0 (New York: Encounter Books, 2013), 54.
 ibid, 27-28.
 Steven Mintz and Susan Kellogg, Domestic Revolutions: A Social History of American Family Life (New York: The Free Press, 1988), passim.
 David Hackett Fisher, Albion's Seed: Four British Folkways in America (Oxford: Oxford University Press, 1989), pp. 274-306; 481-501; 662-680.
 Ibid, 486.
 Mintz and Kellogg, Domestic Revolutions, 43-67.
 Karl Marx and Frederich Engels, "Manifesto of the Communist Party," in Robert Tucker, ed., The Marx-Engels Reader, 2nd ed. (New York: W.W. Norton, 1979), 476.