Swift told People in March 2021:

I’m really proud of [the lyric] ‘She had a marvelous time ruining everything’ from ‘the last great american dynasty’ because it’s about what happens when women step out of their cages and run. It can be a real pearl-clutching moment for society when a woman owns her desires and wildness. And I love the idea that the woman in question would be too joyful in her freedom to even care that she’s ruffling feathers, raising eyebrows or becoming the talk of the town. The idea that she decided there were marvelous times to be had, and that was more important.

On a conversation with Aaron Desner and Jack Antonoff for folklore: the long pond studio sessions, they said this:

Taylor:

I had been wanting to write a song about Rebekah Harkness since 2013, probably, and I’d never figure out the right way to do it because there was never a track that felt like it could hold an entire story of someone’s life and move between generations. Then when I heard the track for “the last great american dynasty”, I was like “oh, my God. I think this is my opening. I think this is my moment. I think I can write the Rebekah Harkness story.”

Jack:

That song is such a folklore moment to me, because it’s not about you but it is all about you.

Taylor:

Well, it’s that Country Music’s narrative device, where in Country Music it’s like “this guy did this, then this woman did this, then they met and their kid was me”, which is the best. You listen to Country songs and you’re just, like, shivers everywhere, my whole body.

Jack:

Even though it’s not til the very end when you spin it around, even though the story is about someone else, I think it’s the most revealing thing. I think it’s so deeply personal. It really hits you in the gut when you hear that at the end.

Swift told Entertainment Weekly:

I learned about her as soon as I was being walked through [her former Rhode Island] home. I got the house when I was in my early twenties as a place for my family to congregate and be together. I was told about her, I think, by the real estate agent who was walking us through the property. And as soon as I found out about her, I wanted to know everything I could. So I started reading. I found her so interesting. And then as more parallels began to develop between our two lives — being the lady that lives in that house on the hill that everybody gets to gossip about — I was always looking for an opportunity to write about her. And I finally found it.