The history of the Roman Catholic Church in the United States in the nineteenth century—when it was still a missionary Church—is a good way to look at transatlantic history from an unusual point of view: the birth and development of Catholic networks, whose goal was to recruit young European seminarians and priests to build new American dioceses. At first, we will show how those networks, which were started during the French Revolution, were grew substantially during the post-revolutionary Catholic revival. Then we will present two case studies. The first one deals with the recruiting methods of Joseph Cretin, a vicar general of the diocese of Dubuque in the 1840’s and the first bishop of St. Paul in the 1850’s, whose use of multiple networks in throughout Europe was not successful. The second case analyses the correspondence between Jean-Marie Odin, archbishop of New Orleans, and the Breton seminarians he visited in 1862 and 1863, which reveals the inner world of these young men and, on an individual scale, the specific interest of these young men to emigrate.