The Mexican Revolution was predominantly a Northern movement. In part this was a logical continuation of what had occurred during the Díaz regime, namely, the rapid development of the northern tier of Mexican states. But in large measure the rise to prominence of leaders such as Francisco Madero, Pascual Orozco, Francisco Villa, Venustiano Carranza, Alvaro Obregón, and Pablo González reflected the advantage they enjoyed over revolutionaries in other parts of Mexico—access to the American border. Arms and ammunition could be imported, loot to pay for these munitions could be exported, United States territory could be used as a base of operations, and the United States provided a sanctuary for the members of defeated factions. Moreover, since the majority of the population along the border were of Mexican extraction, they inevitably became caught up in the factional struggle, as, for that matter, did many of the Anglos, either out of sympathy or because the Revolution became a lucrative business. Yet despite the extent to which the Revolution spilled over into the United States, we still have but a sketchy knowledge of this phenomenon. Precisely how did Mexican juntas function, how were munitions acquired, how was recruiting conducted, and how was revolutionary activity financed? To understand this critical aspect of the Revolution we need much more work along the lines of David N. Johnson's admirable study of Maderista activities in San Antonio in 1910–1911.