In the past couple of decades, Europe and America have taken different paths in how they regulate large firms. American watchdogs largely sat back as big business got bigger, most notably the tech mastodons like Google, Apple and Facebook. Europe, in contrast, felt mega-corporations needed to be kept in check. Its regulators became the world’s most fearsome, none more so than Margrethe Vestager, the EU’s antitrust chief since 2014. Even as Europe failed to come up with tech giants of its own, it was not in California or Washington that Silicon Valley faced most scrutiny, but in rainy Brussels, home to the European Commission.