We need more facts. Are you a US citizen? When did you leave the US? Did you give up your citizenship?
Generally, if you are a US citizen or green card holder, you are required to file a US tax return and pay US taxes on all your world-wide income, no matter where you are living when the income is earned or paid. If you also pay foreign taxes on the same money, you can generally claim a credit or deduction for those taxes on your US return. (As a practical matter, if you never return to the US, the IRS can't audit you or seize your accounts to pay the tax. But if you plan to return, for visits or permanently, you probably need to get your situation in order.)
There are two other special rules I want to point out. (There are probably even more rules, but these are the two I know.)
1. If you are overseas for more than 330 day per year, you can exclude your foreign earned income from US tax. Earned income is income earned from working or providing goods or services. You are still required to pay US tax on unearned income, such as investment and retirement income.
2. There is a special rule for social security. Depending on the country, and if you are retired, you can choose to pay tax on your social security in either the US (where it might be tax free) or your country of residence. This gets tricky and we need more facts.
