The United States was founded on the East Coast as English (and the odd Scottish) colonies with the old cities of Philadelphia, Boston, and New York. These first colonies became the original 13 states. Ever since the 18th century, we have expanded westward into the Ohio Territory, the Northwest Territory, French colonies, Spanish colonies turned Mexico, and then again the British in the Pacific Northwest. (Overly simplified history of the United States’ growth, but it shall do.)
Every ten years, the United States is constitutionally obligated to hold a census. You cannot elect representatives to make political decisions for you if you do not know how many of you there are and where you live. But what these decennial censuses show are how the demographics of the United States have changed, with the population shifting from the East Coast, once almost 100% of the population, to the lands south and west. It’s only natural when you consider how unpopulated that part of the continent is.
But, because we rely on these censuses to redraw political districts and boundaries, every ten years politicians make much ado about…well, something. This article by the New York Times looks at how these changes are set to affect the Midwest in particular and this graphic, while simple, charts the congressional power of the Midwest through the total number of seats held in Congress over the years.