In the Midrash (Shemot Rabbah Parasha 1, Siman 34) it is explained that all the plagues came upon the Egyptians because they sought to destroy a nation that possesses ten virtues. This is the language of the Midrash:

The Holy One, blessed be He, said to Moshe: With the matter in which he (Pharaoh) boasted, and said: "The river is mine" (Ezekiel 29:3), with it I will begin the punishment, as it is written (Exodus 7:25), "And seven days were fulfilled, after the Lord had smitten the river."

After blood, frogs – the Holy One, blessed be He, said: Let something whose growth and sustenance is in water come and punish Egypt, for they sought to destroy a nation destined to receive the Torah, which is compared to water, as it is said (Isaiah 55:1), "Ho, everyone who thirsts, come to the waters."

After this, lice – the Holy One, blessed be He, said: Let something created from dust come and punish Egypt, for they sought to destroy a nation compared to dust, as it is said (Genesis 13:16), "And I will make your descendants as the dust of the earth."

After this, wild beasts – the Holy One, blessed be He, said: Let lions, snakes, and bears come and punish Egypt, for they sought to destroy a nation compared to animals: "Judah is a lion's cub" (Genesis 49:9). "Dan is a lion's cub" (Deuteronomy 33:22). "Dan will be a serpent in the way" (Genesis 49:17). "Benjamin is a ravenous wolf" (Genesis 49:27).

After this, pestilence – the Holy One, blessed be He, said: Let something that causes death come and punish Egypt, for they sought to destroy a nation that sacrifices itself to death for the sanctification of My name, as it is said (Psalms 44:23), "For Your sake we are killed all day long."

After this, boils – "Take handfuls of soot from the furnace" (Exodus 9:8), the Holy One, blessed be He, said: Let what comes from the furnace come and punish Egypt, for they sought to destroy a nation that has sacrificed itself to death: Abraham in Ur of the Chaldees. Hananiah, Mishael, and Azariah in the fiery furnace.

After this, hail – the Holy One, blessed be He, said: Let hail, which is white like snow, come and punish Egypt, for they sought to destroy a nation whose sins I am destined to whiten, as it is said (Isaiah 1:18), "Though your sins be as scarlet, they shall be as white as snow."

After this, locusts – the Holy One, blessed be He, said: Let locusts, which are called "My great army" (Joel 2:25), come and punish Egypt, for they sought to destroy a nation called armies, as it is said (Exodus 7:4), "And I will bring forth My hosts."

After this, darkness – the Holy One, blessed be He, said: Let darkness, which is separated from light, come and punish Egypt, for they sought to destroy a nation that is separated from the nations.

After this, the plague of the firstborn – the Holy One, blessed be He, said: I will pass through Egypt in the middle of the night, and I will punish Egypt, for they sought to destroy the children of Abraham, My beloved, who divided the night to destroy My enemies, as it is said (Genesis 14:15), "And he divided himself against them by night."