By Pavel Polityuk and Natalia Zinets (Reuters) – The port city of Mariupol on the Sea of Azov, reduced to a wasteland littered with bodies by nearly two months of siege and bombardment that Ukraine says killed tens of thousands of civilians, is a big strategic prize for Russia. President Vladimir Putin on Thursday declared the city “liberated” after nearly two months of siege, despite leaving hundreds of defenders still holed up inside the giant Azovstal steel works. Here is why the city matters so much: STRATEGIC LOCATION Mariupol, home to more than 400,000 people before the war, is the bigge…