Before the Israelites had even left Egypt, they began to do what they do best: complain.
They complain when they see the Pharaoh's chariots.
When Pharaoh drew nigh, the children of Israel lifted up their eyes, and, behold, the Egyptians marched after them; and they were sore afraid: and the children of Israel cried out unto the LORD. And they said unto Moses, Because there were no graves in Egypt, hast thou taken us away to die in the wilderness? wherefore hast thou dealt thus with us, to carry us forth out of Egypt? Is not this the word that we did tell thee in Egypt, saying, Let us alone, that we may serve the Egyptians? For it had been better for us to serve the Egyptians, than that we should die in the wilderness. Exodus 14:10-12
They complain when they're starving to death.
The whole congregation of the children of Israel murmured against Moses and Aaron in the wilderness: And the children of Israel said unto them, Would to God we had died by the hand of the LORD in the land of Egypt, when we sat by the flesh pots, and when we did eat bread to the full; for ye have brought us forth into this wilderness, to kill this whole assembly with hunger. 16.2-3
They complain when dying of thirst.
There was no water for the people to drink. Wherefore the people did chide with Moses, and said, Give us water that we may drink. And Moses said unto them, Why chide ye with me? wherefore do ye tempt the LORD? And the people thirsted there for water; and the people murmured against Moses, and said, Wherefore is this that thou hast brought us up out of Egypt, to kill us and our children and our cattle with thirst? 17:1-3
Before long, God will respond to their complaints with several mass murders. But we'll leave that for another time.
Because now it's time for some Holy War.
The Amalekites show up and the fight begins. God controls the whole thing with some remote control magic tricks. Every time Moses holds his hands up, the Amalekites are slaughtered by the Israelites. When he gets tired and lets his arms down, the situation is reversed.
When Moses held up his hand, that Israel prevailed: and when he let down his hand, Amalek prevailed. 17:11
Eventually they had to set some rocks under Moses' arms to make sure that the right people got killed.
But Moses hands were heavy; and they took a stone, and put it under him, and he sat thereon; and Aaron and Hur stayed up his hands. 17:12
But it all worked out just fine.
Joshua discomfited Amalek and his people with the edge of the sword. 17.13
It's too bad, though, that the Bible doesn't say how many Amalekites died in this magical holy war, because now I'll just have to guess.
Oh heck, I'll call it 1000.
But God was far from done with the Amalekites. In fact, he is fighting with them still and commands us all to kill them wherever and whenever we see them.
The LORD said unto Moses, Write this for a memorial in a book, and rehearse it in the ears of Joshua: for I will utterly put out the remembrance of Amalek from under heaven. Exodus 17.14
The LORD hath sworn that the LORD will have war with Amalek from generation to generation. Exodus 17.16
Thou shalt blot out the remembrance of Amalek from under heaven; thou shalt not forget it. Deuteronomy 25:19
So if you happen to see an Amalekite, you know what to do.