 Complete the following phrase:  The Achaemenid occupation of the Indus Valley decreased over successive rulers and formally ended around the time of the Alexanders conquest of Persia. This gave rise to independent kings such as Porus ruler of region between Jhelum and Chenab rivers, Ambhi ruler of region between Indus and Jhelum  rivers with capital at Taxila as well as gaṇa sanghas or republics, which confronted Alexander during his 