or was it more of an overlap of many discriminatory policies, diseases and wars creating the situation where a destruction of native cultures and people happened but wasn't an explicit intentional act of genocide?

Let me go over some brief introductory points so that a more in depth genocide expert can come in and get right to the meat and potatoes of the details:

1. "Genocide" was a term coined by Raphael Lemkin in 1943. "Genocide" could not be a policy that anyone explicitly enacted prior to that point as the word did not exist. Obviously settling parties performed what is, under the 1948 Genocide Convention, considered legal genocide. However it becomes dicey when you want to say, especially w.r.t. the 17th and 18th and even early 19th centuries, that a government 'enacted genocide' as it imposes some kind of responsibility on them that they had some mutual understanding of the concept, had terminology for it laid out, and were purposely in breach of these standards. We must understand that the legal accusation and the modern terminology of genocide frankly did not exist. Therefore everything beyond this point must be acting in some theoretical universe where we can magically apply the modern laws retroactively.

2. What you describe above, if I may in short summarize as the U.S. facilitating conditions where the destruction of the native ethnicity and culture, is legal genocide. Even if in some cases they are not actively enacting the policies if they were conscious of the events occurring in their sovereign territory and did nothing (or whatever courts may determine as 'not enough') to stop it they would also be culpable."

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Let's actually look over the genocide convention which can be conveniently read here. Article II specifically deals with what constitutes as genocidal acts:

 Article II: In the present Convention, genocide means any of the following acts 
                 committed with intent to destroy, in whole or in part, a national, ethnical, 
                 racial or religious group, as such:

(a) Killing members of the group;
(b) Causing serious bodily or mental harm to members of the group;
(c) Deliberately inflicting on the group conditions of life calculated to bring 
     about its physical destruction in whole or in part;
(d) Imposing measures intended to prevent births within the group;
(e) Forcibly transferring children of the group to another group. 

So in that vein: Is 90% of the Native population dying to disease necessarily genocide? No. Are settlers giving smallpox blankets to Natives to bring about their end and free up the land genocide? Yes. Were those 'discriminatory policies' inherently genocidal? No. Was removing Indian children under 'forced assimilation' and putting them in white foster homes to 'raise them white' genocidal? Yes. Are native reservations inherently genocidal? Not necessarily, no. Is forcing large groups of targeted native ethnic groups to relocate significant distances without sufficient materials that would bring about a 'natural death' for the express purpose of taking their land genocidal? Certainly. Some would disagree with me though -- they would say the very principle of herding Natives into reservations and taking all their land for the purpose of recolonizing it for 'better use' and outbreeding them is inherently genocidal.

This is a point that I find many people struggle with and I just need to get out and say outright:

##Genocide can and has occurred even without a single person being killed.

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Though the genocide of the Natives, particularly w.r.t. the United States, is a difficult discussion. It did happen but it was not some centralized plan from the get go. A term my professor used was "episodic genocide" -- which I think the definition of is pretty clear. So there is no 'smoking gun' or some gradual 150 year plan to remove the natives across all states on some federal level but there were a significant amount of isolated incidents that give off a general trend of treatment against the Natives which the Federal and State governments were either active participants in or complicit in allowing to continue.

Ultimately colonization would have its tone set by a series of racial superiority complexes the Europeans had. I like to use one Encri Martinez who in 1606 wrote that Indians and blacks had mental "abilities far inferior to that of Spaniards" and "in Spain a single man does more work in his fields than four Indians will do here." John Mair is also a nice tone setter who in 1519 referred to the Natives on the Caribbean Islands saying they ""live like beasts . . .the first person to conquer them, justly rules over them because they are by nature slaves." The Europeans felt (wrongfully, for that matter) that the Natives were not cultivating the land and using it as 'efficiently' as they could. It was a simple matter of they aren't using it to its best use and we can so we're taking it from them early on and that would be the tone that would shape the next few centuries of colonization.

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Most of my (admittedly pretty intro level) interpretation of this all is coming from Ben Kiernan's work Blood and Soil: A History of Genocide and Extermination from Sparta to Darfur. I must say if you want an absolutely thick discussion of genocidal history this is the book to get -- I've still only been able to tap certain chapters of interest and not complete it all after having it for 5 months.

In my interpretation, yes. For example, in 1863, following the US-Dakota war, many Minnesotans called for the "extermination or removal" of the Dakota and Ho-Chunk in Minnesota. Doing so effectively destroyed their traditional way of life, since the Dakota territory onto which they were forced could not sustain the economic practices to which the Dakota were accustomed. Check out this article, which discusses the Abrogation Act (which unilaterally dissolved all previous US-Dakota Treaties) and the Removal Act (which authorized the deportation of all Dakota from Minnesota). I would argue that such legislation (which, by the way, is still on the books but not enforced) has clear genocidal intent and cannot be construed as anything other than government policy.

Other, more subtle genocidal practices continued into the lives of still-living individuals. The Minnesota Historical Society has performed oral histories with several individuals who attended boarding schools. Many of these can be found [here] (http://collections.mnhs.org/voicesofmn/index.php/10002489). At the boarding schools, one of the main goals was to destroy Native culture in the students. As Richard Pratt, creator of the template for boarding schools said, "Kill the Indian, save the man." Native language, customs, dress, etc. were all forbidden, with physical punishment for those who disobeyed. These schools were also part of government policy.

The extent of the mistreatment of Native Americans has been recognized for a long time. Although the concept of genocide did not exist at the time, Helen Hunt Jackson argues strongly against the government's practices with regards to Native Americans in A Century of Dishonor (1881). What's especially telling about the book, however, is the fact that even as she rails against the government's treatment of Native Americans, she encourages "nicer" genocidal practices. Though she condemns treaty breaking, massacres, and the creation of reservations on the worst land available, she also says that they should be converted to Christianity and integrated into Euro-Americans society. Part of this is simply the lens of the time: capitalist agriculture was viewed as an absolute good, and the opposition of Native Americans to such a life style was seen as a sign of barbarity.

There is, of course, an issue of terminology. Since genocide as a concept was created in the 1940s, any application of it to early US-Native American relations is inherently anachronistic. None of the involved parties would have (or even could have) thought of their actions as "genocidal," which potentially causes problems when arguing for "an explicit policy of genocide." Rather, I would argue that there were several explicit policies which modern observers should recognize as genocidal.

Though there was no industrialized processing of Native Americans as was seen in, for example, the Holocaust, the US government's practices in dealing with Native Americans were created with genocidal intent.