Frédéric Chopin wrote his twin Polonaises, Op. 40, in 1838. These two pieces follow the tradition of the alla pollaca pieces by J.S. Bach, Mozart, and Schubert, by incorporating popular rhythms into a keyboard piece. The Polonaise no. 1 in A major, often nicknamed Military, has been described as a symbol of 'Polish Glory': it is almost entirely played forte or louder, which makes for a bombastic performance. During the September 1939 German invasion of Poland at the outset of World War II, Polskie Radio broadcast this piece daily as nationalistic protest, and to rally the Polish people. The Polonaise no. 2, in C minor, is usually considered the tragic counterpart to the first one.