Share your insights or perspective on the financial matter presented in the input.

US sanctions against foreign citizens 
Are most big US based financial institutions and banks in such a close relationship with USCIS (United States Citizenship And Immigration Services) so they can easily request the information about market traders? Yes. They must be in order to enforce the laws required by the sanctions. What online broker would you suggest that probably won't focus on that dual citizenship matter? "Dual" citizenship isn't actually relevant here. Nearly anyone in the world can invest in US banks except for those few countries that the US has imposed sanctions against. Since you are a citizen of one of those countries, you are ineligible to participate. The fact that you are also a US citizen isn't relevant in this case. I believe the reasoning behind this is that the US doesn't encourage dual citizenship: The U.S. Government does not encourage dual nationality. While recognizing the existence of dual nationality and permitting Americans to have other nationalities, the U.S. Government also recognizes the problems which it may cause. Claims of other countries upon U.S. dual-nationals often place them in situations where their obligations to one country are in conflict with the laws of the other. In addition, their dual nationality may hamper efforts of the U.S. Government to provide consular protection to them when they are abroad, especially when they are in the country of their second nationality. If I had to guess, I'd say the thinking there is that if you (and enough other people that are citizens of that country) want to participate in something in the US that sanctions forbid, you (collectively) could try to persuade that country's government to change its actions so that the sanctions are lifted. Alternatively, you could renounce your citizenship in the other country. Either of those actions would help further the cause that the US perceives to be correct. What it basically boils down to is that even though you are a US citizen, your rights can be limited due to having another citizenship in a country that is not favorable in the current political climate. Thus there are pros and cons to having dual citizenship.