Hello - I'm hoping someone more knowledgable than myself can help a newbie identify this monster weed. It has taken over my garden and has extensive root systems that have become intertwined with the roots of my plants. In this picture it's completely mixed up in a clematis.

If you know this weed, and better yet, know how I can eradicate it (I've tried removing it from the roots but it always comes back), please let me know. Thank you!!