The United States has a highly stringent policy
The United States has a highly stringent policy when it comes to the taxation of its citizens and permanent residents (i.e., those with a green card). The US government taxes all of its citizens based on worldwide income, which means it does not matter where the money is earned.
US persons (including entities) with an interest or signature authority over foreign financial accounts that have an aggregate balance exceeding $10,000 are required to file the FBAR (FinCen 114). The FBAR is separate requirement from your tax return, and failure to file the FBAR carries hefty penalties. With the implementation of FATCA (Foreign Account Tax Compliance Act), foreign financial institutions are providing the IRS with the details of foreign financial accounts held by US persons. As a result, non-reporting is an increasingly risky proposition.
Foreign financial accounts include: bank accounts, brokerage accounts, mutual funds, annuities, life insurance policies with cash value, and indirect interests in financial accounts through a foreign entity (if >50% ownership).