God demonstrated the 10 plagues to:
-the entire nation Israel
-the entire nation Egypt
-the nation Edom
-the nation Ammon
-Moab
-Midian
-Assyria
-Babylon
-the whole land of Canaan
-the Amorites
-Tyre
Everybody knew Who the True God is back then. And everybody knows Who the True God is today.
[Jos 2:9-11 KJV]
9 And she said unto the men, I know that the LORD hath given you the land, and that your terror is fallen upon us, and that all the inhabitants of the land faint because of you.
10 For we have heard how the LORD dried up the water of the Red sea for you, when ye came out of Egypt; and what ye did unto the two kings of the Amorites, that [were] on the other side Jordan, Sihon and Og, whom ye utterly destroyed.
11 And as soon as we had heard [these things], our hearts did melt, neither did there remain any more courage in any man, because of you: for the LORD your God, he [is] God in heaven above, and in earth beneath.