We investigate Yang-Mills theories with arbitrary gauge group on R 3 × S 1 , whose symmetry is spontaneously broken by the Wilson loop. We show that instantons are made of fundamental magnetic monopoles, each of which has a corresponding root in the extended Dynkin diagram. The number of constituent magnetic monopoles for a single instanton is the dual Coxeter number of the gauge group, which also accounts for the number of instanton zero modes. In addition, we show that there exists a novel type of the S 1 coordinate dependent magnetic monopole solutions in G 2 , F 4 , E 8 .