I had a carry over foreign tax credit from taxes paid to Peru and Puerto Rico in 2018. When filing my 2019 taxes the carry over was not used by TurboTax. It seems that when filling in Form 1116 there was no Foreign income entered on line 3d (I did not earn anything in those countries in 2019) so when you divide by 3d ($0) by 3e you know the result. It seems that the only way to utilize a foreign tax credit carry over is to earn future income in that country???