[eschaton]

When it comes down to it, there were two - and in some cases three - different things that contributed to the decline of core cities in the North.

Generalized suburbanization: There was tremendous pent-up demand for housing during the Great Depression and World War II, which would have to have been answered during the period of 1946-1960 no matter what. Even in other countries there was a similar building boom during this period, although in some cases this boom was a bit denser and more transit friendly. And the reason this decline impacted the Northeast/Midwest and not the South/West was mostly because old-line cities ended up surrounded by incorporated suburbs which grabbed the growth, while in the South/West city limits tended to expand to snap up the new suburbs. Old-line urban neighborhoods - where they existed - tended to decline just like in the Northeast/Midwest. So, this period was inevitable.

White flight: This would be the easiest thing to avoid. While a lot of other countries experienced the generalized suburbanization outlined above (particularly Canada and Australia) they didn't experience white flight from the urban cores, which remained largely intact. It's also worth noting within the U.S. that the cities least affected by white flight - places like Seattle, Portland, San Francisco, and Denver - experienced relatively little in the way of blight and tended to recover faster. I don't think it's feasible to avoid white flight without somehow getting rid of the Second Great Migration however. The easiest way to do this would be if the U.S. liberalized immigration policy again post World War II (instead of waiting till 1965) allowing for a mass of postwar European immigrants to staff the growing factories, leaving fewer job opportunities for blacks in the North.

Decline of the Rust Belt: Certain northern cities experienced particular declines related to the destruction of their primary industries, like auto and steel. This was notably different than the other two, because it tended to be felt across the entire metropolitan area, not just the core city. Really this didn't get rolling until the mid 1970s to early 1980s however, which means it was a later process than the "cities going to hell." I think it's plausible any number of cities could have recovered from this earlier. I mean, Boston and NY suffered an earlier industry-related collapse related to the decline of the textile industries (which mostly moved to the South before they moved overseas) and diversified their economies quite well. But not every metropolitan area can be a winner.