I think a pipeline might be involved too?
ETA: or maybe just where the oil gets loaded onto ships.
remember saving pvt ryan. while normandy was were they landed the target was cherbough, dont quote me on spelling dont feel like looking it up. without resuplies the invasion would have failed.
you take a port away from the enemy not only it's easier to resupply your own troops, but you stop 1 way of the enemy to be resupplied. right now russian troops are having problems to resuply their own. but their troops arent even trained for combat. in the end I think russia will take over, but at what cost. russians are protesting in the thousands in russia. this might be the reason putin ends up out of office. at least I hope.