Question: How could God allow such cruelty to befall mankind, such as the ignorant millions in India suffering starvation, pain, disease, etc., brainwashed into a false religion?
Response: I sense the pain of your heart. There are some key words in your important question; the first is, "allow." This is not the world as God wants it to be or made it to be; it is the world that man has made in his rebellion and that God has allowed.
Why would God "allow" sin, suffering, idolatry, etc., all of which will lead to eternal punishment in the Lake of Fire? The biblical answer is clear: He has given man the power of choice. Without free will, we could neither love one another, nor God, nor respond to His love for us. Love is the highest expression of God's character and image in the man whom He created. Obviously, love must come from the heart, or it is not love. The ability to love would be meaningless without the ability not to love and even to hate: obedience is meaningless unless one has the option and ability to disobey.
Rejecting free will, the Calvinist says that this evil world is exactly as God predestined and brings to pass. But the very conscience God has given us will not allow such a wicked charge against God who "is love" (1 Jn:4:8,16), who is "good to all: and his tender mercies are over all His works" (Ps:145:9), and who desires "all men to be saved, and to come unto the knowledge of the truth" (1 Tm 2:4). That many will suffer in the Lake of Fire for eternity is not what God desires for anyone!
Your next key word is "ignorant." On the contrary, God has given each person the witness of creation and conscience. No matter at what time in history or in what place and society anyone is raised (even in the pagan Far East, like India or China, where one-third of earth's population lives), the Bible says that "they are without excuse" (Rom:1:19,20). No one is totally "ignorant"-and to those who obey the light God has given them, more light and grace will be given. But those who reject the light of creation and conscience, which God has given to all, are given up by God to their own willful perversions.
Your third key word is "brainwashed." In fact, no one is a pawn of Satan without first having rejected the light God has given them in creation and conscience. Even then, Satan may need to do little, because "every man is tempted, when he is drawn away of his own lust, and enticed" (Jas 1:14).
The world in Noah's day was so far from what God desired it to be that "it repented the Lord that he had made man, and it grieved him at his heart" to such an extent that He said, "I will destroy man whom I have created from the face of the earth..." (Gn 6:6,7). Indeed, God destroyed everyone except one man and his family, Noah, who "found grace in the eyes of the Lord" (v 8).
Jesus said that in the last days just before His return, conditions on the earth would be as they were "in the days of Noe [and] in the days of Lot" (Mt 24:37-39; Lk 17:26-30). So we know that the world of sin and suffering you describe is not God's doing. Has He allowed it? Yes. But the only other alternative would have been to destroy mankind. We are glad that He did not, because many like Noah have found grace by accepting salvation in Christ Jesus-and there is a new universe coming, entirely without sin or suffering!