Moses had gone up on the mountain and was there for 40 days.
In the meantime, the people at the base of the mountain grew restless. Not willing to wait for him to return with instructions from God, they made their own god out of the gold earrings – a golden calf.

As he is coming down the mountain, Moses meets with Joshua.
And when Joshua heard the noise of the people as they shouted, he said to Moses, “There is a noise of war in the camp.” Ex 32:17

While it wasn’t an attack on the camp, it was the sound of a war. It was the war between righteousness and the sinful nature.

The sinful nature wants to do evil, which is just the opposite of what the Spirit wants. And the Spirit gives us desires that are the opposite of what the sinful nature desires. These two forces are constantly fighting each other, so you are not free to carry out your good intentions. But when you are directed by the Spirit, you are not under obligation to the law of Moses. Gal 5:17-18

The ironic part for the Hebrew’s is the law was just about to be delivered to them. The people were not just worshiping the idol; the sinful nature leads into other areas.

When you follow the desires of your sinful nature, the results are very clear: sexual immorality, impurity, lustful pleasures, idolatry, sorcery, hostility, quarreling, jealousy, outbursts of anger, selfish ambition, dissension, division, envy, drunkenness, wild parties, and other sins like these. Let me tell you again, as I have before, that anyone living that sort of life will not inherit the Kingdom of God. Gal 5:19-21

This internal fight is ongoing. While I consider myself a mature, seasoned Christian, I still struggle.
Where does it come from?

Where do wars and fights come from among you? Do they not come from your desires for pleasure that war in your members? You lust and do not have. You murder and covet and cannot obtain. You fight and war. Yet you do not have because you do not ask. You ask and do not receive, because you ask amiss, that you may spend it on your pleasures. James 4:1-3

The struggle comes from within! It is from temptation. It is from the desire for sinful pleasure.

What is the penalty for sin? The wages of sin is death. Rom 6:23

Moses told them, “This is what the Lord, the God of Israel, says: Each of you, take your swords and go back and forth from one end of the camp to the other. Kill everyone—even your brothers, friends, and neighbors.” The Levites obeyed Moses’ command, and about 3,000 people died that day. Ex 32:27-28

If you are fighting and struggling every day; if you have “war in your camp”, then like the Levites weeding out the idolaters in the camp, you must deal with your own sin nature.
Perhaps this is the reason the apostle said, “I die daily.” 1 Cor 15:31
For he who has died has been freed from sin. Rom 6:7