From the story of Noah and the Ark:
"And GOD saw that the wickedness of man was great in the earth, and that every imagination of the thoughts of his heart was only evil continually." Genesis 6:5

How did this happen?

In the spiritual realm angels exist. God made them too, to serve him. But somehow, some angels became evil - there are no clear scriptures about this - just hints in prophecies. It is clear that there is an evil being who is set against God, and everything God wants to achieve. including

"For all have sinned and fallen short of the glory of God". Romans 3:23

"Our fathers were unfaithful; they did evil in the eyes of the LORD our God and forsook him. They turned their faces away from the LORD'S dwelling place and turned their backs on him." 2 Chron. 29:6

And then shall that Wicked be revealed, whom the Lord shall consume with the spirit of his mouth, and shall destroy with the brightness of his coming: Even him, whose coming is after the working of Satan with all power and signs and lying wonders, And with all deceivableness of unrighteousness in them that perish; because they received not the love of the truth, that they might be saved. And for this cause God shall send them strong delusion, that they should believe a lie: That they all might be damned who believed not the truth, but had pleasure in unrighteousness. 2 Thes. 2:8-12

Jesus told Paul:- To open the unbeliever's eyes, and to turn them from darkness to light, and from the power of Satan unto God, that they may receive forgiveness of sins, and inheritance among them which are sanctified by faith that is in me. Acts 26:18

But they mocked God's messengers, despised his words and scoffed at his prophets until the wrath of the LORD was aroused against his people and there was no remedy. 2 Chron. 36:16

"But they refused to pay attention; stubbornly they turned their backs and stopped up their ears. They made their hearts as hard as flint and would not listen to the law or to the words that the LORD Almighty had sent by his Spirit through the earlier prophets. So the LORD Almighty was very angry.
" 'When I called, they did not listen; so when they called, I would not listen,' says the LORD Almighty. Zech. 7:11-13

He who does what is sinful is of the devil, because the devil has been sinning from the beginning. The reason the Son of God appeared was to destroy the devil's work. 1 John 3:8

This I say therefore, and testify in the Lord, that you henceforth walk not as other unbelievers walk, in the vanity of their mind, Having the understanding darkened, being alienated from the life of God through the ignorance that is in them, because of the blindness of their heart: Who being past feeling have given themselves over unto lasciviousness, to work all uncleanness with greediness. Ephes. 4:17-19

Romans 3:10-18
As it is written, There is none righteous, no, not one: There is none that understands, there is none that seek after God. They are all gone out of the way, they are totally worthless; there is none that does good, no, not one. Their throat is an open grave; with their tongues they have used deceit; the poison of asps is under their lips: Whose mouth is full of cursing and bitterness: Their feet are swift to shed blood: Destruction and misery are in their ways: And the way of peace have they not known: There is no fear of God before their eyes.

Psalm 14 and Psalm 53
For the director of music. Of David.

The fool says in his heart, "There is no God."
They are corrupt, their deeds are vile;
there is no one who does good.

The LORD looks down from heaven on the sons of men
to see if there are any who understand, any who seek God.
All have turned aside, they have together become corrupt;
there is no one who does good, not even one.

Will evildoers never learn--
those who devour my people as men eat bread
and who do not call on the LORD?
There they are, overwhelmed with dread,
for God is present in the company of the righteous.
You evildoers frustrate the plans of the poor, but the LORD is their refuge.
Oh, that salvation for Israel would come out of Zion!
When the LORD restores the fortunes of his people,
let Jacob rejoice and Israel be glad!

Proverbs 1:22-33
"How long will you simple ones love your simple ways?
How long will mockers delight in mockery
and fools hate knowledge?
If you had responded to my rebuke,
I would have poured out my heart to you
and made my thoughts known to you.
But since you rejected me when I called
and no one gave heed when I stretched out my hand,
since you ignored all my advice
and would not accept my rebuke,
I in turn will laugh at your disaster;
I will mock when calamity overtakes you--
when calamity overtakes you like a storm,
when disaster sweeps over you like a whirlwind,
when distress and trouble overwhelm you.

"Then they will call to me but I will not answer;
they will look for me but will not find me.
Since they hated knowledge
and did not choose to fear the LORD,
since they would not accept my advice
and spurned my rebuke,
they will eat the fruit of their ways
and be filled with the fruit of their schemes.
For the waywardness of the simple will kill them,
and the complacency of fools will destroy them;
but whoever listens to me will live in safety
and be at ease, without fear of harm."

Genesis 3:17-19
To Adam he said, "Because you listened to your wife and ate from the tree about which I commanded you, 'You must not eat of it,'
"Cursed is the ground because of you; through painful toil you will eat of it all the days of your life.
It will produce thorns and thistles for you, and you will eat the plants of the field.
By the sweat of your brow you will eat your food until you return to the ground,
since from it you were taken; for dust you are and to dust you will return."

Genesis 4:9-12
Then the LORD said to Cain, "Where is your brother Abel?"
"I don't know," he replied. "Am I my brother's keeper?"
The LORD said, "What have you done? Listen! Your brother's blood cries out to me from the ground. Now you are under a curse and driven from the ground, which opened its mouth to receive your brother's blood from your hand. When you work the ground, it will no longer yield its crops for you. You will be a restless wanderer on the earth."