On the 27th April 1509, Pope Julius II excommunicated the entire republic of Venice. Having been elected pontiff six years previously, Julius II was determined to reclaim Italian territory that had been gradually taken by Venice throughout the fifteenth and early sixteenth centuries.
Having joined together with France, Spain, and the Holy Roman Empire to form the League of Cambrai in December 1508, the Papacy was ready to mount military action to seize control of the Romagne region from Venice. Shortly before invading, however, the Pope issued the interdict against the Republic that excommunicated every single one of its citizens.
The interdict deprived the Venetians of their spiritual salvation, and was therefore a formidable weapon. When Venetian forces were defeated at the Battle of Agnadello the following month, the Republic entered what was referred to by one contemporary as a ‘foul mood’.
Peace negotiations were concluded on February 24th the next year, at which point the interdict against Venice was lifted. France and the Holy Roman Empire, however, were keen to maintain their advance. Having underestimated his former allies, the Pope sought to stop the French advance that was threatening the Papal States. Amazingly he formed a new alliance with Venice and Spain, and placed France under papal interdict. By the time he died in 1513, Julius II had therefore fought and formed alliances with France, Spain, Venice and the Holy Roman Empire. That’s quite some diplomacy.