belmont married caroline slidell perry, the daughter of matthew calbraith perry, on 7 november 1849. soon, john slidell, his wife's uncle, starting helping belmont. belmont's first task was to campaign for james buchanan in new york. in june, 1851, belmont wrote letters to the "new york herald" and the "new york national-democrat", insisting that they do justice to buchanan's presidential run. but franklin pierce won the nomination instead, and belmont made large contributions to the democratic party. after his victory, pierce in 1853 appointed belmont "chargé d'affaires" and minister to the hague. while in holland, belmont urged american annexation of cuba as a new slave state in what became known as the ostend manifesto.