Victory of the Romans over the Persian nation

غُلِبَتِ ٱلرُّومُ

The Roman Empire has been defeated-

فِىٓ أَدْنَى ٱلْأَرْضِ وَهُم مِّنۢ بَعْدِ غَلَبِهِمْ سَيَغْلِبُونَ

In a land close by; but they, (even) after (this) defeat of theirs, will soon be victorious-

فِى بِضْعِ سِنِينَ ۗ لِلَّهِ ٱلْأَمْرُ مِن قَبْلُ وَمِنۢ بَعْدُ ۚ وَيَوْمَئِذٍۢ يَفْرَحُ ٱلْمُؤْمِنُونَ

Within a few years. With Allah is the Decision, in the past and in the Future: on that Day shall the Believers rejoice-