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<p>I don’t have firm data, but it is much more difficult to get a job in defense as a non-American. Not impossible, but definitely harder. You have to be a much stronger candidate simply because the employer has to jump through a lot more hoops to get you in and it has to be worth their time and money. If you have proven yourself to be brilliant, then it is less of a problem, but if you are just an average or slightly above average engineer, you are going to get passed up in favor of someone from the US.</p>