Original: Siena's republic, struggling internally between nobles and the popular party, usually worked in political opposition to its great rival, Florence, and was in the 13th century predominantly Ghibelline in opposition to Florence's Guelph position (this conflict formed the backdrop for some of Dante's Commedia).
Simplified: Siena's republic, struggling internally between nobles and the popular party, usually worked in political opposition to its great rival, Florence.