 Complete the following phrase:  In his later years of rule, Peter the Great found himself in a strong enough position to increase Russian influence more southwards in the Caucasus, the Caspian Sea and the Black Sea, challenging both the Safavids and the Ottomans. He made the city of Astrakhan his base for his hostilities against Persia, created a shipyard, and attacked the weakened Safavids in the 