It was to Walpole's opposition that the Peerage Bill owed its defeat; and this success forced his rivals again to admit him, with Townshend, to a share in the Ministry, though they occupied subordinate offices. But this arrangement was soon to yield to a more natural one. The sudden increase of English commerce begot at this moment the mania of speculation. Ever since the age of Elizabeth the unknown wealth of Spanish America had acted like a spell upon the imagination of Englishmen, and Harley gave countenance to a South Sea Company, which promised a reduction of the public debt as the price of a monopoly of the Spanish trade. Spain however clung jealously to her old prohibitions of all foreign commerce; and the Treaty of Utrecht only won for England the right of engaging in the negro slave-trade with its dominions and of despatching a single ship to the coast of Spanish America. But in spite of all this, the Company again came forward, offering in exchange for new privileges to pay off national burdens which amounted to nearly a million a year. It was in vain that Walpole warned the Ministry and the country against this "dream." Both went mad; and in 1720 bubble Company followed bubble Company, till the inevitable reaction brought a general ruin in its train. The crash brought Stanhope to the grave. Of his colleagues, many were found to have received bribes from the South Sea Company to back its frauds. Craggs, the Secretary of State, died of terror at the investigation; Aislabie, the Chancellor of the Exchequer, was sent to the Tower; and in the general wreck of his rivals Robert Walpole mounted again into power. In 1721 he became First Lord of the Treasury, while his brother-in-law, Lord Townshend, returned to his post of Secretary of State. But their relative position was now reversed. Townshend had been the head in the earlier administration: in this Walpole was resolved, to use his own characteristic phrase, that "the firm should be Walpole and Townshend and not Townshend and Walpole." [Sidenote: Walpole's Ministry.]