Are America and Europe Dar al-Harb, and is it permissible for a resident of an Islamic country to deposit his money in a usurious bank therein for benefit, and is there a detailed study on this matter?

Usury (Riba) is absolutely forbidden in a Muslim land and elsewhere, according to the majority of scholars. It is not permissible to deposit money in interest-based banks except out of necessity, and when no Islamic banks are available. Depositing money in interest-based banks is not permissible even if no interest is taken on it, because it involves cooperating in sin and aggression. However, if a Muslim fears their money will be lost and finds no way to preserve it except by depositing it in an interest-based bank, then it is permitted for them to do so without taking interest. The usurious interest obtained from depositing money in an interest-based bank must be disposed of.