The promise of Allaah is always true and will definitely occur!
Allaah (The Most High) said:
سَنُرِيهِمْ آيَاتِنَا فِي الْآفَاقِ وَفِي أَنفُسِهِمْ حَتَّىٰ يَتَبَيَّنَ لَهُمْ أَنَّهُ الْحَقُّ ۗ أَوَلَمْ يَكْفِ بِرَبِّكَ أَنَّهُ عَلَىٰ كُلِّ شَيْءٍ شَهِيدٌ
We will show them Our Signs in the universe, and in their ownselves, until it becomes manifest to them that this (the Qur’an) is the truth. Is it not sufficient in regard to your Lord that He is a Witness over all things? [41:53]
[سَنُرِيهِمْ آيَاتِنَا فِي الْآفَاقِ – We will show them Our Signs in the universe]: The (Islamic) conquest of the furthest regions of the earth. [وَفِي أَنفُسِهِمْ – and in their ownselves]: The conquest of Makkah.
This is the statement of Al-Hasan, Mujaahid and Sadiy (rahimahullaah)
[Source: Zaadul Maseer’ by Imaam Ibnul Jawzi (rahimahullaah)]