Just moved into a new place and this plant seems to be taking over most of the planting area and seems to be choking some of the other trees and plants around it. I'm about to aggressively prune it down but wanted to know what kind of plant it was - whether it will flower, and whether there is any reason for me not to drastically reduce it. (The thorns hurt as well)
I think you have a Common Buckthorn (Rhamnus cathartica). The leaf shape looks right, oval-shaped and serrated with short petioles. And the thorns definitely look like buckthorn, surprisingly long and pretty sharp.
In most of the Eastern United States (which is where your profile says you are) Buckthorn is considered an invasive species, it has few natural predators here, it forms dense thickets where it gets a foothold and it's berries are not a very good food-source for birds, though they will eat it if desperate. If you find it annoying, I would suggest cutting it back as hard as you feel like, even up to total removal.