Answer:
Then the LORD saw that the wickedness of man was great in the earth, and that every intent of the thoughts of his heart was only evil continually. (GENESIS 6:5).
DEUTERONOMY 9:1-4, PSALM 14:2-3, 2 PETER 3:7, ROMANS 10:13
Our verse from Genesis tells us two very important things—that people of the earth were wicked and that God knows all the thoughts and intents of man’s heart. It seems like the Israelites killed innocent people. But we need to learn a couple of things here.
First, there are no innocent people . . . the Bible clearly says that we all have sinned against a holy and just God. Second, God did not only allow the Israelites to kill the people, He commanded them to do it. Because God is holy, He needs to judge sin and wickedness. He used the Israelites to judge the people and remove the evil in the land.
We know there are still evil, wicked people today. But God doesn’t command us to destroy those people in the same way. That is because Jesus Christ died on the cross. God judged the sin in the world by punishing His Son on the cross. The Bible tells us that God Himself will judge those who do not claim Jesus Christ as their Savior—those who do not receive Jesus’ free gift of forgiveness and who refuse to trust Him and believe in Him as the one and only way to heaven.
Source: https://answersingenesis.org/kids/god/israelites-kill-people/