Despite the popular narrative that the United States is a "land of mobility," the country may have become a "rooted America" after a decades-long decline in migration rates. This article interrogates the lingering question about the social forces that limit migration, with an empirical focus on internal migration in the United States. We propose a systemic, network model of migration flows, combining demographic, economic, political, and geographic factors and network dependence structures that reflect the internal dynamics of migration systems. Using valued temporal exponential-family random graph models, we model the network of intercounty migration flows from 2011 to 2015. Our analysis reveals a pattern of segmented immobility, where fewer people migrate between counties with dissimilar political contexts, levels of urbanization, and racial compositions. Probing our model using "knockout experiments" suggests one would have observed approximately 4.6 million (27 percent) more intercounty migrants each year were the segmented immobility mechanisms inoperative. This article offers a systemic view of internal migration and reveals the social and political cleavages that underlie geographic immobility in the United States.

翻译：尽管美国常被描绘为“流动之地”，但经历数十年迁移率下降后，这个国家可能已成为“根深蒂固的美国”。本文探究了限制迁移的社会力量这一悬而未决的问题，并以美国国内迁移为实证焦点。我们提出一个系统性迁移流网络模型，融合人口、经济、政治及地理因素，并纳入反映迁移系统内部动态的网络依赖结构。通过使用加权时态指数随机图模型，我们对2011至2015年间县际迁移流网络进行建模。分析揭示了一种碎片化固化模式：政治环境、城市化水平和种族构成差异显著的县之间，迁移人数显著减少。采用“剔除实验”检验模型发现，若该固化机制失效，每年将有约460万（27%）的额外县际迁移者。本文为国内迁移提供了系统性视角，并揭示了美国地理固化背后的社会与政治分歧。