Globalisation accelerated genuinely dramatically in the late twentieth century, falling trade barriers, cheaper transport and communication, and increasingly integrated financial markets together let capital, goods and production move across national borders faster and more easily than ever before. That same acceleration is exactly what generated the political backlash the term's discontents refers to, since the benefits and costs of that new mobility landed on genuinely different groups of people in genuinely different ways.
Trade liberalisation, cheap shipping and instant communication together drove the acceleration
Successive rounds of international trade agreements steadily lowered tariffs and other trade barriers through the late twentieth century, while the container shipping revolution made moving physical goods across oceans dramatically cheaper and faster, and improving telecommunications and eventually the internet let businesses coordinate production and services across huge distances almost as easily as across a single city. Together, those three separate developments made it genuinely practical for a company to relocate manufacturing to wherever costs were lowest, in a way that simply hadn't been logistically realistic a few decades earlier.
The resulting gains and losses were distributed in genuinely different patterns, which is where the backlash came from
Globalisation's benefits, cheaper consumer goods, new export markets, were spread broadly across entire economies but relatively thinly per person, while its costs, factory closures and job losses tied to production moving elsewhere, landed sharply concentrated in specific industries and specific towns and regions. That mismatch, diffuse broad gains against sharply concentrated local losses, is exactly why globalisation could genuinely raise aggregate economic measures for a whole country while still generating real, geographically concentrated political backlash from the specific communities that bore its costs most directly.
What we're still unsure about
That globalisation accelerated sharply in the late twentieth century, and that its costs and benefits were distributed in genuinely different patterns, is well established, extensively documented economic history. What's more genuinely a matter of active, ongoing economic debate is exactly how large a role globalisation itself played in specific regional job losses compared with automation and technological change happening at the same time, since the two trends are genuinely entangled in the same time period and industries, and economists continue to actively disagree about how to cleanly separate their respective contributions rather than treating that separation as a settled empirical question.
This sits inside Globalisation & Its Discontents, one of seven topics in Contemporary History, one of seven domains in History, one of seventeen subjects the app can quiz you on.