An article by Werner Weinberg answers the question, "Why did you not leave Germany when you had time", of those Jews who remained even after the Crystal Night. Weinberg mentions that emigration was difficult to impossible before the Crystal Night, and outright impossible afterward. He says that there were quotas, ludicrously expensive visas, and various other regulatory blocks to just go from Germany to most nations on the planet. While Weinberg gives numerous reasons why individuals either chose not to leave or were incapable of leaving, I feel it necessary to state a simple answer to the question: state control was ubiquitous.
I am not one to treat bigotry as the cause of a policy, because there are far more serious issues to consider, such as outright murder, kidnapping, rape, and imprisonment. The Holocaust was an atrocity (at best) because it involved so much criminal activity. What made it so much worse was the fact that the already-normal controls that nation-states had on immigration made the atrocities even easier. Afterall, when a set of something is physically concentrated, it is easier to gather them up for destruction.
What we may treat as normal made up the long list of excuses for what ended as Jews and other state-hated groups in concentration and labor camps.
First, there is the immigration controls. Weinberg states very clearly that Britain, America, France, and other countries simply refused to allow anymore Jews to enter legally beyond various arbitrary limits. After the Crystal Night, you couldn't even leave Germany illegally. The rest of the nation-states acted as guardsmen for the Nazi regime by helping the German state to keep German Jews in Germany. The Nuremburg trials were a farce because those states that organized it were complicit in keeping Jews in Germany. It could only be more obviously farcical if the guards of the concentration camps had organized the trials.
Second, states are widely considered to be the legitimate definers of what is legal and illegal. This is the foundation of any state-run genocide, whether against a religious/cultural group in Germany or a tribe in Africa, because the color of law is the first excuse for every added aggression, whether increased regulations or mass-murder. The soldiers, the police, the courts, the juries, the legislators, and sometimes the Press readily support aggression on the part of the state, because it is the state that is calling the shots. "Shoot the Jews", "Yes, sir!" "Shoot the Tutsi", "Yes, sir!"
Immigration controls are tighter than when Hitler ran the German state, yet none are weary of the prospects for genocide. For if few can leave when bigots are on the rise to power, then many more will be swallowed in future, state-run genocides than otherwise. "But having open immigration policies would lead to a weakening of national security," says the politician of [insert any polity here]. That betrays two condemning bits of information: (1) the state can't secure the nation against threats that are inside of the nation, and (2) increasing the risk of an attack upon oneself is somehow sufficient justification to block immigration.
When the nation-state is considered the greatest protector of humanity in a given nation, it is hilariously pathetic that a common justification for immigration control is security. Imagine if the city police where you live decided that the only way that they can fight crime in the city was to control who can and cannot enter the city. "The city is too easy to be invaded by criminals, so we have unfortunately decided that we must now create check-points at all roads that enter the city and turn away all who do not have approval to enter the city." The criminals already inside the city may cheer on such a policy, because the cops would be spending less time actually fighting crime.
Now imagine that all nearby cities create similar policies. Now it is trivial for the city government to begin a campaign of persecution against a group of residents, because that minority has nowhere to go. Of course, many might state that it was the wrong policies or even the wrong people in office that made the immigration controls and persecution possible. Such a position treats the state as a benign organization who merely occasionally gets bad leaders, thus provides no understanding as to why genocides are so easy.
Yes, genocides are easy because of the state, and are likely most easy today because states have access to more advanced technology and thus more advanced methods of surveillance and control. Imagine if all you had to do to achieve one of your goals was to be elected to an office and write a few pages of text. Other people would be paying for and organizing the achievement of your goal, all because you were in that office and gave a particular order. Even if an additional barrier to achieving your goal was a committee-based organization, wouldn't this be a very attractive means of achieving your goal? For such a means does not require that you pay anything; you only need write and talk in such a way that people will declare their support. Abracadabra, your goal is on its way to being achieved.
Now imagine that your goal is to ruin the lives of a minority. The process is the same; you just have to find some way to make the genocide sound like it isn't diabolical. That is why propaganda is so commonly employed by the state; they have to find some way to make people think that the genocide, or whatever terrible policy, is somehow good or necessary.
When someone says, "genocide can't happen here, not in the land of the free and brave," respond with this: "agents of the state bravely and freely upheld slavery in America, which would've qualified as genocide if so many slaves hadn't survived the state-supported brutality." It has already happened here and it is now easier than ever.