Another popular explanation for the Italian Renaissance is the thesis, first advanced by historian Hans Baron, that states that the primary impetus of the early Renaissance was the long-running series of wars between Florence and Milan. By the late 14th century, Milan had become a centralized monarchy under the control of the Visconti family. Giangaleazzo Visconti, who ruled the city from 1378 to 1402, was renowned both for his cruelty and for his abilities, and set about building an empire in Northern Italy. He launched a long series of wars, with Milan steadily conquering neighbouring states and defeating the various coalitions led by Florence that sought in vain to halt the advance. This culminated in the 1402 siege of Florence, when it looked as though the city was doomed to fall, before Giangaleazzo suddenly died and his empire collapsed.