Immigration policy in the US can be very broadly broken down into two eras, demarcated roughly by the turn of the twentieth century, and distinguished by the state’s orientation towards immigration restriction. The first period, which stretches back to the colonial era, oversaw a generally open regime, in that international migration was largely unrestricted. Some state laws provided for the exclusion of “undesirable” migration — including the poor, and convicts — into their territories, but on a federal level, what legislation existed regarding immigration was focused on stimulating migration or regulating the conditions under which migration occurred,9 rather than controlling or restricting the flow of migration. The second period, where federal law explicitly regulated the flow itself, began to emerge towards the end of the nineteenth century as immigration law became centralized in the federal government, and more importantly, moved from the assumption of admission (barring some ground of exclusion) to an assumption of exclusion (unless the migrant specifically qualifies for admission).