Re: First sign of a downturn
"US got a one-off artificial boost with Trump's tax breaks last year "
Cycles aside, every time the USA has elected a populist president (twice in the 19th century and once in the 20th) there was a short term uptick in the economy and then a crash with prolonged recession.
The 1870 crash/recession affected Europe so badly that it stayed in recession whilst the USA went through another boom/bust cycle with a crash in 1890. That didn't ease until 1903. Hoover did the same thing (although it's arguable this policies may have been effective if he'd been given another six months, as things were turning as he went out)
It's fairly expected that the USA is going to crash again as it didn't fix the problems which led up to 2008 (that crash were pretty predictable when the spam for house and car loans started pummelling servers in the late 1990s. Offering credit to people with a history of defaults isn't a good move) or the problems and extreme hardship at the bottom end that have been caused since (Being poor isn't usually the poor person's "fault", so stop treating them like it is. That's how you breed criminality and extremism) - and with a populist president at the helm giving payoffs to his rich cronies (tax breaks) it's likely to crash _hard_ and stay that way for quite a while. This is why so many people have been jittery about a trade war on top of that.
The next decade is going to be "interesting" as in the kind of history period you'd prefer to study, not live through.