Key instances where God punished the Israelites include:
Worship of the Golden Calf (Exodus 32): After Moses was on Mount Sinai, the people created a golden calf to worship. As punishment, God ordered the Levites to kill about 3,000 people.
Complaining at Taberah (Numbers 11:1-3): The people complained about their hardships, and the Lord sent fire that burned the outer edges of the camp.
Craving Meat (Numbers 11:4-35): After complaining about the lack of meat and being tired of manna, God provided a massive amount of quail but also sent a severe plague that killed many people due to their gluttony and lack of trust.
Miriam and Aaron's Rebellion (Numbers 12): When Miriam and Aaron challenged Moses's authority, God punished Miriam with leprosy for a period of seven days.
Refusal to Enter the Promised Land (Numbers 14): The most significant punishment occurred when the people, out of fear after hearing the spies' report, refused to enter the Promised Land and wanted to return to Egypt. God sentenced that entire generation of adults (except Joshua and Caleb) to die in the wilderness, wandering for 40 years. The ten spies who brought the bad report were struck down by a plague and died immediately.
Korah's Rebellion (Numbers 16): Certain leaders, including Korah, rebelled against Moses's and Aaron's leadership. God caused the earth to open up and swallow the main offenders and their families, while a subsequent plague killed 14,700 people who sided with the rebels.
Complaining about Lack of Water (Numbers 21:4-9): The people complained again about the lack of water and food. God sent poisonous snakes (fiery serpents) into the camp, which bit the people, and many died.
Idolatry at Peor (Numbers 25): The Israelites engaged in sexual immorality and worshipped the Midianite god, Baal of Peor. This resulted in a plague that killed 24,000 people.