This is one of the series of 3 paintings painted by Paolo Uccello to commemorate the Florentine victory against Siena (both cities in Italy now, but then, Italy was not a united country). 4000  cavalry men and 2000 infrantry fought for Florence. The cause? Just regular rivalry between two emerging Italian city-states. What is weird is that in the Sienese chronicles, they considered themselves to be victorious too. Go figure.

 The other two paintings showing the beginning and end of war are in The National Gallery in London and the Uffizi in Florence. The painting in the Louvre shows an army ready to fight - the guy with a rearing horse is giving a signal to attack. All of the knights are wearing hats which are typical in Florence. Even though he was a pioneer or perspective in painting and inspired such airtists as Leonardo da Vinci and Albrecht Durer to use it, Uccello doesn't use it in these particular series. He was obsessed with representing pure form and his works fascinated the 20th century cubists. 

The painter, Paolo Uccello was not only an artist, but also a mathematician, who did important work on perspective in art. He left no school of followers though. Uccello was his nickname because he loved painting birds. He was born to a noble mother and a barber/surgeon father. He was great buddies with Donatello.

The 3 paintings were commissioned by a Florentine Lionardo Bartollini Salimbeni who was a key player in the war with Siena.