When it comes to Foreign Military Sales, I fully understand why a nation might decide to trade with the US in lieu of another nation from a foreign policy perspective. But I don't understand what political advantage exists when it comes to dealing with the US when it comes to direct commercial sales. So, here's my question:

Why do foreign nations chose to trade with the US when it comes to DCS? 
If the US stopped selling X nation small arms, what would stop them from buying those arms from a third party (i.e. Russia/China)?

Maybe there are some resources you can point me to? 

I want to make sure you are familiar with the resources at the Forum on the Arms Trade: https://www.forumarmstrade.org/hspolicydebate.html. 

Here are  some quick responses

Why do foreign nations chose to trade with the US when it comes to DCS? 

For pretty much all the same reasons as for FMS... DCS deals are ultimately approved by the federal government, so purchasers typically expect the same quality, support and notional partnering with the US.
 
If the US stopped selling X nation small arms, what would stop them from buying those arms from a third party (i.e. Russia/China)?

This is a version of a question we get all the time. See https://www.forumarmstrade.org/faqvideos.html for some experts responses as well as the section on the core HS resource page we've made. There are certain differences in each arms market, and if you are asking about "small arms" in particular, the Small Arms Survey is a good resource on that market writ large. This is somewhat a hot topic right now (the admin's effort to make it easier to sell firearms.) Resource page on that at https://www.forumarmstrade.org/catitoiii.html
 
Maybe there are some resources you can point me to?  

See above for starters

I'm researching export controls on hypersonic missiles. I was inspired by this link, however I've run into few problems that I can't seem to find answers to:
1. Does the U.S have any plans to sell hypersonic missiles to other countries? If not since they probably don't now, do you think the U.S ever will or has the desire to sell to allies?
2. Do you think Russia and China follow-on is true if the U.S implements export controls? Will Russia and China also implement export controls if the U.S does?
3. Will hypersonic missiles be a substantial part of the arms market in the future? Or will this be a niche weapon that the US tries to control?
Thanks for you time and any help is appreciated!

So far as I know, the US has no plans to export the new breed of hypersonic missiles. (Existing ICBMs are, of course, hypersonic missiles, and we don't export those.) At present, the proposed hypersonic missiles are still in development, so there's nothing to export as yet in any case. But even when they are deployed, I can't imagine that they would be exported as they are likely to be considered cutting-edge weapons that give the US an advantage we wouldn't want to share. Now, maybe down the road, a decade or two from now, in a more hostile world, we might consider exporting them (or the technology to make them) to, say, the UK, but that's speculative.

Likewise, I can't imagine Russia or China sharing their cutting-edge hypersonics technology to anyone else.

From what I’ve read, I think it may be still too early days to know if the US plans to sell hypersonics. A recent NYT article states that “In 2018, Congress expressed its consensus in a law requiring that an American hypersonic weapon be operational by October 2022. This year, the Trump administration’s proposed defense budget included $2.6 billion for hypersonics, and national security industry experts project that the annual budget will reach $5 billion by the middle of the next decade. The immediate aim is to create two deployable systems within three years. Key funding is likely to be approved this summer.”
 
So to me, it doesn’t sound like the timeline and production scale would allow for sales in the near term and from a strategic perspective, I would be surprised if the US would want other countries to have these given the military advantage they offer. In some ways, they strike me as what it must have been like to acquire nuclear weapons when they were first developed, from the perspective of deterrence and power. To your other questions, I would normally say that the same types of logic and agreement that the nuclear powers operate on (“we’re allowed to have these weapons because we are responsible states, but others cannot obtain them”) could apply to hypersonics but given how poor relations are right now between these countries I’m not sure they’d all agree to be bound by export control limitations.
 
I’d encourage you reach out to others and keep reading. SIPRI is an extremely reliable source of information, and it has done some solid research in this area too:
 
https://www.sipri.org/sites/default/files/Factoring-Russia-into-US-Chinese-equation-hypersonic-glide-vehicles.pdf
 
https://sipri.org/commentary/topical-backgrounder/2017/chinas-calculus-hypersonic-glide
 
France is also reportedly interested in their acquisition: https://www.defencetalk.com/race-for-hypersonic-weapons-heats-up-as-france-joins-fray-72093/

There have been a couple related articles you might want to check out, if you've not seen.

https://www.nytimes.com/2019/06/19/magazine/hypersonic-missiles.html 

https://www.armscontrol.org/act/2019-06/features/arms-race-speed-hypersonic-weapons-changing-calculus-battle

I was recently looking through the topic wording and technology regarding missile defense peaked my interest. I was told by another member of the community that ballistic missile defense technology was not categorized as "arms." 

In my brief reading through topic literature, I cannot find anything that speaks in a particular direction. It appears to me that most BMD systems use surface to air missiles, which I would think fall under category four on the USML. However, I cannot find any explicit reference to these operating systems being classified as arms under US code.

The controlling document, at least as explained to me, the AECA, was written well before the explosion of missile defense technologies during the 80s and afterward. I was wondering if you could point me toward any definitions of what constitutes arms sales or sales of arms that definitively create a distinction that allows missile defense to either be considered or not considered a sale of arms.

Thanks for your query. Alas, you've been misinformed, at least to some extent. Ballistic missile defense systems certainly are considered as arms and you'll see many sales falling under the foreign military sales (FMS) and direct commercial sales (DCS) programs. To date, the largest single FMS notification under the Trump administration has been for Terminal High Altitude Area Defense (THAAD) equipment, support, and services to Saudi Arabia. See the Forum's resource page and google spreadsheet for many other missile defense sales.

You can also find some more discussion of specific missile defense sales from the United States and more globally in this recent publications:

William Hartung and Christina Arabia, "Trends in Major U.S. Arms Sales in 2018: The Trump Record - Rhetoric Versus Reality," Center for International Policy, April 2019.

Aude Fleurant +, "Trends in International Arms Transfers, 2018," SIPRI, March 2019. (see box 1)

On April 4, 2019, Iain Overton's The Price of Paradise: How the Suicide Bomber Shaped the Modern Age was published. The Forum on the Arms Trade interviewed Overton (Executive Director, Action on Armed Violence [AOAV]) to ask about key findings, ways to think about suicide bombings, and suggestions for how to approach curbing their frequency. His answers are featured in this Looking Ahead blog entry. ​ ​Question: What are the trends you are finding?

The most notable fact – and the reason I wrote the book – has been that of a major shift towards suicide bombing use, especially in the last decade both in terms of attacks and casualties. More than 40% of all people killed by suicide bombers since their first use against the Tsar of Russia in 1881 have happened in the last five years.
 
This is in large part because of a major spike in attacks by Salafist jihadists. Such a dark trend has, though, deep historical roots.  In the book I argue that ISIS is, effectively, the sum of the parts of previous suicide bomb campaigns.  It has elements of the utopianism of the Russia revolutionaries of the 19th century; the militarism of the Japanese kamikaze; the Islamic notion of sacrifice as developed in Iran under the Ayatollah Khomenei; the strategic logic of Lebanese terror groups; the targeting of civilians as seen by Hamas; the cult of the leadership as seen under the Tamil Tigers; and the millenarianism and global conflict as summed up by Al Qaeda.  In addition to this, though, modern day Salafist jihadist suicide bombers have a profound sense of ‘end of days’ – a millenarian logic that means, to those bombers, death is loved more than life and their sacrifice is integral to the creation of a glittering Islamic future.

This is right.  The suicide bomber does not fit neatly into international arms control and, as such, it is the ever-growing elephant in the room. It is the deadliest of all improvised explosive devices (IEDs), and IEDs themselves are the cause of the greatest civilian harm of all explosive weapons – at least since 2010.
 
IEDs themselves pose a fundamental challenge.  After all, only about 15% of all victims from landmines and ERW have, in recent years, been from the traditional manufactured landmine, but the global approach to landmines has not changed substantially in response to this.
 
Suicide bombs rely on improvised components.  Some component parts - such as detonators and certain chemicals – certainly need more attention in terms of international border sales control.  But it goes deeper than just precursor control.  Overall, the suicide bomber offers up an existential crisis to some degree to the UN and the disarmament community.  The solution cannot be to ban production.
 
Furthermore, modern day suicide bombers use ideology as a weapon that, in itself, poses challenges for members of the disarmament community who have impartiality rooted in their DNA. 
 
I believe one reason for the proliferation of this form of weapon is that it side-steps UN arms controls; it doesn’t fit neatly into funding streams to challenge its spread; it is largely ignored in places such as the Convention on Certain Conventional Weapons (CCW) and [UN General Assembly] First Committee; and it doesn’t have strong voices among civil society seeking to address its harm. 
 
The reasons for these short-comings are understandable and complex, but given the harm from suicide bombers, the silence that surrounds the suicide bomber in terms of high-level debate at the UN and elsewhere is deafening.  Responses to it are not coordinated and where they are, they are often under-funded and under-valued.
 
In a sense the complexities of challenges that the suicide bomber poses to the disarmament community is, in part, one of its devastating strengths. And those who say the existing processes are already in place to stop such a terrible weapon from spreading, should follow up their statement by saying that those processes are clearly not working.

There are many individual and group steps taken on the path to most suicide bombings. These are complex and diverse.  Some involve individual motivations of revenge, depression, hopelessness and fear.  Some involve groups believing in utopianism, militarism, sacrificial justice, the right to target civilians and the need to attack those they deem heretics and apostate.
 
But just as there are many steps to a suicide bomber, there need to be steps away from such as well.
 
To prevent calls by those who might use bombs to act out of revenge, nation states need to uphold human rights; they need to ensure that breeding grounds for extremism are not created in prisons, schools or mosques; they need to combat Islamophobia; to insist that the trials and punishments of Muslims accused of terror are subjected to a transparent and fair process; to address high levels of unemployment and widespread socio-economic deprivation among many Muslim communities; to create victim-assistance programmes; and to recognise the fact that many societies around the world have concerns about immigration and the failures of liberal policies on race and religion.

This list could go on. Countering extremism on all sides is notoriously hard. When the then Secretary-General Ban Ki-moon revealed the UN’s plan of action to do so in January 2016, there were over seventy recommendations made, ranging from development policy initiatives, to youth empowerment, to gender equality to human rights.

But there are four fundamental points that I believe should be addressed head-on.

The first is that the United Nations needs to up its game. A ban on suicide bombing would send out a clear message of priorities, and create political commitments and funding to address the complex issues that underpin the weapon’s rise. This needs to spread beyond demining operations – any approach has to accept suicide bombings are built upon both social and ideological grounds. And funding could help charities, businesses, trade officials, police units, UN agencies, militaries and others come together to respond imaginatively and creatively to this terrible weapon. Without there being a coherent and systemic approach to combating the cult of the suicide bomber, there is little hope the spread of this weapon will be curtailed. 

The second point is that we should seriously assess the impact Western foreign policy has had on the Middle East and North Africa to avoid past mistakes. This does not mean accepting the conspiracy-laden narratives presented by jihadists. Nor is it realistic to assume that Western policies towards the region going back for decades can be completely altered. But the inadvertent arming of future jihadi groups through the US’s and other states’ oftentimes uncontrolled supply of arms and explosives to the Middle East should be stopped. Air strikes have been shown, repeatedly, to fuel support for Salafi-jihadism, while carrying out secret drone strikes bolsters the claims the West is waging an eternal, subversive battle against Islam. These must be ended.

The third challenge lies in stopping the conflicts in which the vast majority of today’s suicide bombings and their casualties are found. Some nation states have focused on state-building activities to do this, with some in the West initiating violent regime change to induce democratisation and economic growth. They do so believing peace can be built by creating democracies, but after two decades this approach has failed to work. Partly this is because you cannot export democracy down the barrel of a gun. Partly because such interventions fail to take into account the political reality of the Middle East, specifically the Arab states. Traditional Arab-Islamic concepts of war and peace seem more based on immediate conflict resolution, seeking a return to the status quo, than wholesale transformation and reform. Peace-building initiatives need to reflect the cultural conditions of the region, and not merely act as a ‘sticking plaster’ of Western sensibilities.

Fourth, states should be profoundly aware of the failures of history when it comes to countering suicide bombers. Much of the media might seek hard and retributive justice, but history has shown that man’s ability to overstep the mark, generate mission creep and abuse human rights in the name of national security is all too predictable. The conditions to produce a suicide attack are complex: the means to counter such attacks need to be as well. 

In the end, it is in our own responses to suicide attacks where we have the most significant capacity to act. When we look back to find out how we arrived at the place we find ourselves in now, we should not be blinded by the carnage brought by terrorism, but also see the ensuing violence justified to crush that threat. We must remind ourselves how the Tsar’s blind repression of anarchists fanned the flames of tyrannical Communist revolt. How the US high command’s justification for the devastating use of nuclear weapons to defeat the feared kamikaze ushered in the Cold War. And how the calamitous invasions of Iraq and Afghanistan were decided before the dust had settled on downtown Manhattan.

That suicide bombing campaigns have often had, through history, singular characteristics and these can be traced from its first inception to the modern day. That stating suicide bombing is a Muslim problem fails to recognise that the Russians invented suicidal terrorism, the Chinese invented the suicide belt, the Russians used suicide bomb planes before the Kamikaze, that the Sri Lankans were once the deadliest users of suicide bombs in the world, and that – throughout history – Christians, Buddhists, Sikhs and others have all used this form of terror. Ideology is a driving force behind suicidal terror, but that ideology is not unique to Salafist jihadism.