Yep, one of the milkweeds.

Asclepias incarnata, Swamp Milkweed

I'm assuming the spread, is the roots underground. If it was from seed, I'd consider Asclepias curassavica. Both species have similar leaves and pods.

A, incarna self-seeds regularly, too; not to the taking-over-the-garden level, but I get a couple new plants every year.

...and the flower color is probably a deep orange, red, and/or yellow.