Photos app gets stuck when deleting photos on my MacBook

This morning I imported some photos (6,500 of them) from my iPhone. I wanted to put them on an external hard drive. The only method I could figure out was to import them into the Photos app on my MacBook, export them from the Photos app onto the hard drive, and then delete them from my Photos library on my MacBook.

I was successful on all counts except the last. Each time I try to delete a photo (whether it's 1 at a time or 1,000 of them), the app gets stuck on the "deleting photos..." dialogue box indefinitely. The only way I know of to get out of that screen is to force quit the Photos app.

I would love to delete the photos from my MacBook in order to free up the 30+ GB of space they take up, as my hard drive is a 256GB model. Any ideas/fixes?

I couldn't find another post of somebody having this problem...