How world order changes

CAMBRIDGE - After the Berlin Wall came down in 1989, and almost a year before the Soviet Union collapsed in late 1991, US President George H.W. Bush proclaimed a “new world order.” Now, just two months into Donald Trump’s second presidency, Kaja Kallas, the European Union’s top diplomat, has declared that “the international order is undergoing changes of a magnitude not seen since 1945.” But what is “world order,” and how is it maintained or disrupted?