Overall, US citizens and Green Card holders are required to file a US Federal Tax Return each year if their income is over the minimum threshold. No matter where you have earned this income, what currency it is earned in, or whether you have also paid taxes in the country in which you reside, you are required to file in the US if your income is above these levels.
The thresholds are currently:
Single with income over $13,850
Married filing jointly with income over $27,700
Married filing separately with income over $5
Self-employed individuals need to file if their income is over $400
Head of Household is over $20,800
Note: You may need to file state taxes as well as taxes for your small business operating overseas. Depending on your situation, you may also be required to file additional reports including Form 8938 and the Foreign Bank Account Report (FBAR or FinCEN Form 114) to report assets held overseas.