Okay so I'm new to these forums and new to new to working on my car, so excuse my ignorance. About a month ago I bought a 1990 Civic DX hatchback with 206,000 miles. I figured it would be a good starter car to introduce myself to DIY and general mechanic work. The car runs great, has some rust and for the most part is fine but there are some issues.
This is the most pressing one, whenever I brake at high speed the rear of the car vibrates rather violently, the faster I'm going the worse it is. If I brake harder it gets slightly better but not much.
My immediate assumption is that the rear drums are warped so I replaced the rear drums and shoes but that didn't change anything. A friend of mine told me that maybe because the frame is weakened due to rust maybe I need to stiffen up the frame, I recently ordered some strut and tie bars and they should arrive in a few days but I'm not sure thats the real problem. Someone else told me that my wheel bearings may be bad but I don't know enough about cars to know if this makes sense.
Do either of these solutions make sense or can anyone think of anything else that might fix this problem? Thanks a lot.

Your sure it's coming from the rear?, if not the front rotors could be warped as well, or the wheels are out of balance. Just a thought.