After doubling during the 19th century, Florence's population was to triple in the 20th, resulting from growth in tourism, trade, financial services and industry.
During World War II the city experienced a year-long German occupation (1943–1944) and was declared an open city. The Allied soldiers who died driving the Germans from Tuscany are buried in cemeteries outside the city (Americans about nine kilometres south of the city, British and Commonwealth soldiers a few kilometres east of the centre on the right bank of the Arno). In 1944, the retreating Germans blew up the bridges along the Arno linking the district of Oltrarno to the rest of the city, making it difficult for the British troops to cross. However, at the last moment Charle Steinhauslin, at the time consulate of 26 countries in Florence, convinced the German general in Italy that the Ponte Vecchio was not to be blown up due to its historical value.
Instead, an equally historic area of streets directly to the south of the bridge, including part of the Corridoio Vasariano, was destroyed using mines. Since then the bridges have been restored to their original forms using as many of the remaining materials as possible, but the buildings surrounding the Ponte Vecchio have been rebuilt in a style combining the old with modern design. Shortly before leaving Florence, as they knew that they would soon have to retreat, the Germans murdered many freedom fighters and political opponents publicly, in streets and squares including the Piazza Santo Spirito.
In November 1966, the Arno flooded parts of the centre, damaging many art treasures. Around the city there are tiny placards on the walls noting where the flood waters reached at their highest point.
In November 2002 was the place of birth of the first edition of the European Social Forum.