The boom of buying US capital earkt 1990 had its own reasons, primarily it was Japan, which had a balloning real estate market (sound familiar?). Some of the assets purchased at the time were more status than useful (like historical buildings) or for purchase of rival US companies manufacturing semiconductors and related equipment, machine tools and some other industries, not a good thing at all! The subsequent hangover after the Japanese real estate bubble burst, plus backlash from the US were key reasons for the following crash in capital investment.
Also, the 1999 crazy buy dot com everything boom was not sustainable either, that's the 2000-2001 hangover on the chart. I would argue that a lot of this investment boom and bust from 1990 - 2007, is not the norm. And unfortunately, for the 2004-2007 boom, some of that was investment in some AAA's that went bad.....If the boom and busts are smoothed out it would be interesting to see what the progression was.