A--- Yes, He is Able to do so as He Himself showed in His Glorious Qur'an saying, {And had Allah willed, He could have made you (all) one nation, but He sends astray whom He wills and guides whom He wills. But you shall certainly be called to account for what you used to do}. (Al-Ma'idah, 48 & An-Nahl, 93)

Allah the Almighty says: {And had your Lord willed, those on earth would have believed, all of them together}. (Yunus, 99)

But, that which He did to them is the requirement of His Wisdom, and the sign of His Lordship, Worship and Names and Attributes. Thus, whosoever says: "Why are there - from among His slaves -the obedient and the disobedient?" This is just like his saying: "Why are there among His Names: the Harm Inflicting and the Benefit Giver, the Giver and the Preventer, the Humiliator and the Raiser, etc." As His Acts are the requirements of His Names and the effects of His Attributes. Thereupon, objecting to His Acts, is like objecting to His Names, Attributes, Worship and Lordship: {Glorified is Allah, the Lord of the Throne, (High is He) above all that (evil) they associate with Him! He cannot be questioned as to what He does, while they will be questioned}.

(Al-Anbiya', 22, 23)