> What drove the worldwide populist uprising?
In America, it's easy to see why, if you're actually willing to pay attention to the complaints of the white working class. They are tired of being exploited for tax money while not receiving anywhere near the entitlements of other groups, tired of not being officially in the civil rights legislation, tired of their communities being flooded with foreigners that don't share their values, and tired of being replaced. Opiate crisis, brain-drain taking all the youth away from small towns, Walmart destroying Main Street, and other phenomena have combined to make much of America a desolate shadow of its former glory.
A lot of this is the direct outcome of policy decisions nobody agreed to. Nobody would have agreed to the 1965 Hart-Cellar act if they had known that the result would be the end of American culture as they knew it.
Such an uprising was inevitable and it will continue to get more strident as long as the actual concerns of these people are brushed off or claimed to be offensive concepts. It's not a matter of being "left behind", it's a matter of being replaced.