I'm going to try and give you something of a simplified oversight because the history of race and ethnicity in the western world (and in general) is extraordinarily rich and complex, and I don't want to get too bogged down into debates and discussions peripheral to your interest.

I guess my question is really what has given rise to our current understanding of what constitutes a "race", and why is it generally only broken down along black vs white vs asian vs native

You've hit onto something incredibly important and significant here. 'Race' as we generally understand it in the western world, and especially as it is understood in North America, is generally defined by a spectrum ranging from dark skin to light skin - but there is no reason why it must be that way. Race is a social construct, a means of classifying people based on perceived defining physical characteristics; it would be just as easy, as you possibly hint to in your example, to have a racial paradigm that places people on a spectrum of perceived characteristics from 'Most Asian' to 'Least Asian', rather than 'White' to 'Black'. For that matter, we could just as easily have socially constructed groupings of people based on all manner of other characteristics, and we do. Gender and sexuality are similarly constructed social identities. It is not difficult to imagine a world where we group people by height or eye colour in a similar fashion.

One of the fundamental problems with socially constructed categories like race is that they are inevitably to some extent arbitrary. If you took everyone in the world and lined them up according to a spectrum that ranged from light skin to dark skin, with the intent to split the world half and half, it would be extremely difficult to categorise a vast swathe of people in the middle of the line. That is true no matter how simple or complex our understanding of race is. If we try to break that same line up into twenty sub-categories, we would still have a very difficult time determining where the dividing lines for those categories should be. The same is true for gender or sexuality; when we try to categorise Human beings based on physical characteristics, even if those characteristics have obvious biological causes (like skin colour), there will always be a huge number of exceptions that defy the rules we try to create.

Now, I'll talk about the distinction between race and ethnicity in a bit. First though, I'll try to explain the experience of race in the US context you're writing about.

One of the remarkable things about race as a pervasive system of classification is that it is a relatively new social construct in the grand scheme of Human history. The notion of race as we understand it today in the western world only really begins to appear from the 16th and especially 17th Century onwards. People have been aware that Human skin colour and physical traits varied for a very long time before this, but it's only really from the 1500s onwards that we begin to see the conceptualisation of these differences into systems of racial classification. This also happens to be - and not without coincidence - the period of western history in which we see the beginning of the transatlantic slave trade on a meaningful scale.

In terms of the English conception of racial hierarchy, this very much has its origins in the English culture of the 17th Century. The people they encountered with such suddenness in their explorations of Africa were thoroughly 'unenglish' - their perceived sexual morality, standards of living and their religious practices all stood in sharp contrast to the virtues English civil society cherished and lauded. African civilisation was perceived to be barbaric and beastly by most contemporary English observers, in some kind of fundamental way; from the early days of European-African encounter we find comparisons being drawn between African people and apes in a fashion not unlike that we see in particularly sickening kinds of racist discourse today. English culture at the time already had also developed a notion that black was bad - that blackness was synonymous with dirty, filth and decadence whilst white represented purity and goodness.

Now, English society could not be described as racist in the sense we know it today. These early sentiments were not unanimous, nor were they well developed - there was no ideology that explicitly drew a link between worth and skin colour yet, but there was a pervasive negative attitude towards blackness and towards the qualities associated with African culture in white English minds. Within this culture of negativity there was still room for positivity, for rejection of prejudice, and for black people to find acceptance; white minds were not yet firmly fixed against all black people. Yet it is this pre-existing cultural negativity that does ultimately come to give rise to our modern conception of race, made inevitable by the social and economic developments arising out of exploration of the New World.

In short, before slavery became a meaningful institution, the British were already using forced labour in their colonies - specifically, white indentured labour. Indentured labour was based on the same kind of principles that underpin systems of economic apprenticeship, with the notion that white workers would voluntarily go to the New World (as you might guess it wasn't always very voluntary), work for a period of years and then be rewarded with the means to make a successful life for themselves thereafter. At times, the conditions of these servants could very much come to resemble slavery; particularly in parts of the British Caribbean. Some people make the argue that it was effectively a form of early slavery. Yet this system of labour was being used at a time when the notion of personal freedom and rights was in ascendancy in England, and England had gradually brought an end to systems of traditional bondage there by this time. There were limits to how far it could be pushed as an institutional system of exploitation and domination (though some made a damn good effort!). Likewise, there were efforts at Native American slavery; see this thread for more on that aspect.

At the same time, the Portugese and Spanish trade in African slaves was well under-way. African slaves began to arrive in British colonies, first in small numbers then in large. From the 1640s onwards, Britain begins to take up an enthusiastic role as an importer of African slaves. A demand for increasingly large quantities of unfree labour intersected with pre-existing negative attitudes towards Africans and blackness in general to begin to give rise to a new, especially insidious and derogatory form of unfree labour that, by the dawn of the 18th Century, had firmly entrenched itself as slavery. Race in the American and Caribbean context in essence emerges from a vicious cycle whereby demand for exploitable labour and existing prejudice reinforce each other, gradually creating a paradigm in which 'black' is synonymous with 'slave'; whereby a condition of degraded Humanity cannot be separated from the skin colour of its victims. Ideas of 'white' and 'black' emerge in contrast to one another, as both rationalisations and ramifications of slavery.

One of the long-term consequences of this is that the United States has developed a notion of race that is, quite literally, black or white. Traditionally in American racial discourse you are either black or you are white; the United States is remarkable for how absolutely rigid its system of racial classification is. The idea that you can be mixed race, that you can occupy a place between the two positions as an authentic identity, is really quite a novelty in American culture. Historically, if a black woman had a child by a white man, her child was seen as black - and this is a notion that has its origins in slavery, where your status as a free person or an enslaved person was based on the status of your mother, no matter how light or dark your skin was. This is contrast to the rest of the Americas where the construction of race has been very different; in both Brazil and the Caribbean, the distinction between black and white was never made so strong. Rather, the experience there has been to view race as a spectrum ranging from white to black, with many possible identities and configurations along the way. Chinese and Indian migration in the late 19th Century further complicated and added additional nuance to the British Caribbean's conceptions of race, especially in Trinidad and Tobago.

One of the challenges this paradigm has created for the United States is that other racial groups do not fit into it very well at all. According to the 2010 Census for instance, there are more Hispanic people than there are African Americans - but there are more African Americans than there are 'White' Hispanic people. Hispanic and Latino people do not easily fit into the traditional racial discourse of the United States - their classification or identity is more complex than just 'black' or 'white'. Likewise, we know plenty of groups who are very clearly white but who never benefited fully from the implication of 'whiteness'; anti-Irish sentiment is well documented for instance. It is as a result of challenges like this that we see an increasing distinction between race and ethnicity (not just in the US, either). Racially, you can be black or you can be white; ethnically, you can be Hispanic or non-Hispanic. Ethnicity becomes a framework through which we can try to rationalise the very obvious inadequacies of racial classification whilst still retaining that system as a valuable category of Human beings.

(Part 1 of 2)