To the uneducated, this is a pretty purple flowering weed growing in wet, swampy areas in SE Michigan (I found references to it growing in Maryland and elsewhere).
To the educated, it is a highly invasive non-native plant that threatens native wetland species. It can reduce biodiversity, eliminate food sources for marsh animals and change water flow patterns.
There are several websites that will describe methods of control or elimination. I have never seen any attempts of control or elimination around our stick built home. Maybe, because it is so pretty??