If Allah had willed, He would have made all of Humanity one Nation Allah says:وَلَوْ شَاء اللّهُ لَجَعَلَكُمْAnd had Allah willed, He would have made you,meaning - O mankind,أُمَّةً وَاحِدَةً(all) one nation,This is like the Ayah:وَلَوْ شَأءَ رَبُّكَ لامَنَ مَن فِى الاٌّرْضِ كُلُّهُمْ جَمِيعًاAnd had your Lord willed, all of those on earth would have believed together. (10:99),meaning, He could have created harmony among them, and there would not be any differences, conflicts or hatred between them.وَلَوْ شَأءَ رَبُّكَ لَجَعَلَ النَّاسَ أُمَّةً وَاحِدَةً وَلَا يَزَالُونَ مُخْتَلِفِينَإِلاَّ مَن رَّحِمَ رَبُّكَ وَلِذلِكَ خَلَقَهُمْAnd if your Lord had so willed, He would surely, have made mankind one Ummah (nation or community), but they will not cease to disagree. Except him on whom your Lord has bestowed His mercy, and for that did He create them. (11:118-119)Similarly, Allah says here:وَلكِن يُضِلُّ مَن يَشَاء وَيَهْدِي مَن يَشَاءbut He allows whom He wills to stray and He guides whom He wills.وَلَتُسْأَلُنَّ عَمَّا كُنتُمْ تَعْمَلُونَBut you shall certainly be called to account for what you used to do. i.e. on the Day of Resurrection, He will ask them all about their deeds, and will reward or punish them even equal to a scalish thread in the long slit of a date stone or the size of a speck on the back of a date stone, or even a thin membrane of the date stone.The Prohibition on taking an Oath for Purposes of Treachery Allah says