Yet these same researchers would not think of driving to New York, Texas or California, and upon arrival at the first large city inquire at city hall or just any church to see if they have records of a Nolan family who lived somewhere in that state about a hundred years ago. That, in essence, is what so many of us do in our genealogical quests. Go to your local library and find American history books. Look at the dates on your family tree. Look at the places where your families lived and forget about specifically finding your John Z. Schmidt in Wisconsin after the Civil War.
Every subject has a history.
The secret is learning how to focus on the subjects that will enable you to track down those elusive, wandering ancestors. Your family's history is unique, so you will have to sift through many sources and put the pieces together. It won't be handed to you in a neatly printed package. There is no magic place to write to that has your genealogy. Most libraries have this reference set and you can then order a specific book through interlibrary loan.