The New World arc is less about specific 'events' and more about a fundamental shift in the story's very structure. Before, you had clear sagas with defined end points—defeat Crocodile, reach Enies Lobby, survive the Summit War. Now, the narrative sprawls like the sea itself. Big Mom's tea party, the Whole Cake Island chaos, the revelation of Luffy's Gear Fifth during the Onigashima raid... these aren't isolated incidents. They're interlocking pieces of a massive power play involving emperors, the World Government, and ancient history. The lines between 'arcs' blur completely.
To me, the defining through-line is the collapse of the established order. The fall of Doflamingo wasn't just taking down a Warlord; it broke the underworld's economy. The Levely summit exposed the fractures between kingdoms. Kaido's defeat sent a shockwave that’s essentially redrawing the geopolitical map of that world. It’s a constant escalation where every victory creates three new, bigger problems. You can't really point to one event as 'key'—it's the cascading domino effect of them all that defines this phase of the journey, where the stakes are finally as vast as the Grand Line promised they would be.