Well if you wanted to travel legally to the Americas, you would have needed a license from the Casa de Contratación, the branch of the government which oversaw all of the emigration to the Americas (as well as legal trade, the flotas, official maps, and the licensing of ships, captains, and pilots among other things). The specific requirements for getting this license changed over time (as did the loopholes), but they can be basically summed up here. The Crown generally viewed emigration to the Americas as problematic because it depopulated Spain and opened the Americas up to the negative influences of certain populations of Spanish society. Thus, the emigration process reflected these concerns. Migrants had to prove they were of pure blood...so not a converso (convert of Judaism) or a morisco (convert from Islam). The Crown prefered single men, so they required married men and women to get special permission from the Crown itself. If you were married and bringing your wife, it was necessary to prove that your marriage was legitimate and that the woman was also of pure blood and of good moral character. This meant that officials traced your lineage and general life history by looking through baptism and marriage records, copying them into your file, and having a notary certify that they had been faithfully copied. Applications were often accompanied with witness testimony about the the lineage or about the moral character of the person. It was expected that a migrant had an official reason for going: taking up a government post, being a soldier, having a trade reason, or possessing a religious post among others. The Contratación section of the Archivo General de Indias is filled with these applications, each of which could be short (sometimes just a few pages of handwritten material) or long if there was a legal dispute or a longer investigation. The general idea was that your identity would be known to the state, so the applications recorded the migrants’ birthdate, parents, family members, occupation, and even their physical descriptions of each person. As a migrant, you would have had to provide information about where you were going to settle and for how long. You could not be a foreigner (although there were still many who made it to Spanish America with many cities having sizable foreign populations), and you could not have been convicted by the Inquisition (this was important for keeping the Americas free of Reformation heresies [although there was lots of that too]) or convicted by secular courts for any serious crimes. A migrant might also try his or her luck signing up for expeditions or settlement projects, where you might have been questioned by officials involved in the expedition rather than royal officials.

Once a person received the license from the Casa de Contratación, it was necessary to secure passage to the Americas, usually by paying an exorbitant fee on board some ship sailing out of Seville, the only officially legal port for sailing or doing business with the Americas (until the 1700s). The legal process and its high fees made migration to the Americas out of reach of most common people. Therefore, estimates for how many Spaniards moved to the Americas are generally low. There seem to have been between 500,000 and a million Spanish immigrants over the course of the entire colonial period, with about 250,000 of those occurring in the sixteenth century at an average rate of 2,000 to 2,500 per year.

The reason why we can’t really say for sure how many people actually emigrated was because there was TONS of other ways to cross the Atlantic through quasi-legal and illegal methods. The sheer number of complaints about restricted groups reaching the Americas spaced out over hundreds of years is impossible to ignore, and the Crown frequently updated their licensing rules to clamp down on illegal crossings and established various commissions to determine who was coming and how they were getting there and institutions like the Inquisition to enforce religious orthodoxy of those who managed to sneak across.

Nonetheless, the off-the-books flow of common people and “undesirables” appears to have been constant. Sailors, artisans, and poorer people found passage on ships that needed sailors. Individuals used their connections to find passage and sometimes changed their names or went by aliases to sneak across (that was part of the reason that in order to get a license, a physical description of the applicant was included to prevent people from impersonating another person). Individuals might stowaway on a ship (usually with the knowledge and help of ship captains or other sailors). A stowaway might act as a part of the crew and carry out various ship tasks. These quasi-stowaways/sailors jumped ship when they reached the Americas. Or they might have joined the crew and continued to travel on board the ship to some other port where they had social connections. Or they might work in the Americas for a while and later move (or sail on board the many small trading ships and fishing vessels that plied the seas) to another population center or follow some other opportunity that arose through their ever-changing social networks.

The requirements and high costs of completing an application also meant that it was difficult for many poorer people to get licenses for family members. I have read a number of bigamy inquisition cases where the man told interrogators that he tried to get his wife a license to travel with him but couldn’t secure one. After years of being separated without news of his spouse, the man remarried. Or sometimes the defendant claimed that another friend, family member, or sailor told him that his first wife was dead. Eventually, he showed up in the Inquisition documents because he got caught being double married.

Another common way to get to the Americas was to become a servant of someone who had a legal permit to cross to the Americas. Huge numbers of domestic servants and assistants in various capacities (both men and women) cross the Atlantic this way.

However, the numbers of all the Atlantic crossers (both legal and illegal) pales in comparison to the number of enslaved Africans who were forcibly migrated across the Atlantic. Enslaved Africans were far and away the largest group of people to cross the Atlantic prior to 1810. Thus, the colonial population of the Americas was much much darker than we realize today. Many ports and urban centers in the Americas were majority black, and the influence of African cultural and intellectual systems were certainly present in the daily life of common people in the colonial world.