The city of Phoenix began in 1870. The first buildings were made with whatever materials they could get. Adobe was still being used, but money was being invested in brick and wood, which although of very poor quality, was very expensive. And while these buildings looked good at the time, they needed to be replaced by 1890, 1900 at the latest. And to help this building boom, the railroad had arrived and along with that much better quality building materials.
So, if you grew up in Phoenix in the 1870s, and returned in 1905, you would have hardly recognized your old town. Phoenix has always been wildly successful, and the old buildings were torn down and replaced with new ones as fast as possible.
The next big change in the face of Phoenix came with the prosperity of the 1920s. This building boom, which of course including tearing down all of the old buildings, lasted until the stock market crash of 1929. There was still some tear-down-and-replacement going on in the early 1930s, but not much. And during World War II, in the 1940s, Phoenix didn't change much.
After World War II, starting in 1947, Phoenix did its largest growth spurt ever. In fact, most people consider Phoenix to have begun in the late forties or early 1950s. It's not surprising, as the new buildings obliterated once and for all the vast majority of what Phoenix had looked like in its previous eighty years. Tear-down-and-building slowed in the 1960s and 1970s, in spite of efforts to "revitalize" areas.
The next big tear-down-and-build started happening in the mid-90s. At that point, there were still a lot of old, very run-down buildings that went back to the prosperity of the 1920s and 1950s. But decades of hard times in Phoenix had turned most of these buildings into places that no one in their right mind would want to live, or work, in. Yes, they were very nice in the 1920s, and 1950s, but like an old car that had been neglected, there really wasn't much value in them any more.
Pictured above: The Anderson Building in 1901, northwest corner of Washington and 1st Street, Phoenix, Arizona. It replaced a lot of old buildings that had been there since the 1870s.