But before this conclusion had been reached a significant incident justified the foresight of Calhoun. Towards the close of the campaign, a proposal made in Congress to grant to the Executive a large supply to be expended during the recess at the President's discretion in purchasing Mexican territory was met by an amendment moved by a Northern Democrat named Wilmot, himself an ardent supporter of the war, providing that from all territory that might be so acquired from Mexico Slavery should be for ever excluded. The proviso was carried in the House of Representatives by a majority almost exactly representative of the comparative strength of the two sections. How serious the issue thus raised was felt to be is shown by the fact that the Executive preferred dispensing with the money voted to allowing it to be pushed further. In the Senate both supply and condition were lost. But the "Wilmot Proviso" had given the signal for a sectional struggle of which no man could foresee the end.
Matters were further complicated by a startlingly unexpected discovery. On the very day on which peace was proclaimed, one of the American settlers who had already begun to make their way into California, in digging for water on his patch of reclaimed land, turned up instead a nugget of gold. It was soon known to the ends of the earth that the Republic had all unknowingly annexed one of the richest goldfields yet discovered. There followed all the familiar phenomena which Australia had already witnessed, which South Africa was later to witness, and which Klondyke has witnessed in our time. A stream of immigrants, not only from every part of the United States but from every part of the civilized world, began to pour into California drunk with the hope of immediate and enormous gains. Instead of the anticipated gradual development of the new territory, which might have permitted considerable delay and much cautious deliberation in the settlement of its destiny, one part of that territory at least found itself within a year the home of a population already numerous enough to be entitled to admission to the Union as a State, a population composed in great part of the most restless and lawless of mankind, and urgently in need of some sort of properly constituted government.