While humans ate tons of carbs since agroculutural revolution those carbs were ~95% glucose (starch), eg potato, grains, rice, beans,...
Only in the last ~70 years did we have an explosion in
1) sugar (50% fructose) and HFCS
2) fruits with a high sugar content: most modern fruits didn't exist ~100 years ago, and those that did had a fraction of fructose that modern fruits have.
Fructose is known to be the most destructive things you can put in the body (glucose is almost harmless compared to it).
Eg a study shown that replacing or even just replacing fructose with glucose had a massive improvement in fatty liver in children in just 9 days!
Fructose is metabolized like alchocol, which is why in the ~1970 or 1980 you start seing T2 diabetes and fatty liver in children, while before T2 diabetes and fatty liver was only a problem of alchoholics.