 Complete the following phrase:  The Bug was part of the frontier between the slices of Poland occupied by Austria and Russia after the Third Partition of Poland in 1795, the southern half of the eastern border of the Duchy of Warsaw 1809-1815, Congress Poland 1815-1867, of the Vistula Land 1867-1913, and of the Regency Kingdom of Poland 1917-1918. The Bug also formed part of the dividing line between German Wehrmacht and Soviet Red Army zones specified in a secret clause of the 