Why were the Hebrews in Egypt’s bondage to begin with?

A pivotal moment in Israel’s history is the deliverance from Egypt. Why did G-d have them put there in the first place?

“And He said to Abram, “You shall surely know that your seed will be strangers in a land that is not theirs, and they will enslave them and oppress them, for four hundred years. And also the nation that they will serve will I judge, and afterwards they will go forth with great possessions.” – Bereshit 15

In other parts in the Bible, Israel is punished for violating the law, but what did Israel do before Egypt for G-d to put them there? From this passage alone, I can only think that it was for the purpose of obtaining possessions (???). There was clearly an intentional purpose for the bondage. What was it?

(I wish to understand more. I promise I mean no disrespect.)

Thanks and Shalom!