After which event did God harden Pharaoh's heart?

The event after which God hardened Pharaoh's heart is specifically associated with the fifth plague on the cattle. In the book of Exodus, this plague involved a severe disease that affected the livestock of the Egyptians, while the Israelites' livestock remained unharmed. Following this devastating blow to the Egyptian economy and way of life, the scripture indicates that Pharaoh's heart was hardened by God, further leading him to resist the plea of Moses to let the Israelites go.

This act of hardening Pharaoh's heart serves to demonstrate God's sovereign authority over the situation and serves as a precursor to the Israelites' eventual liberation. It reinforces the theme of divine intervention for the purpose of showing His power and fulfilling His covenant promises.

Other events listed in the options were pivotal in their context but are not specifically noted in scripture for the act of hardening Pharaoh's heart at that particular moment. The purpose of God hardening Pharaoh's heart is an important theological point, illustrating how resistance to God's will can lead to a greater display of divine power and purpose.