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Keyword here "was" so not "is". It was destroyed. Mariupol is an Ukranian loss, but not much of a Ruzzian win. Steel is produced all over the world and is pretty much in crisis in Europe because it is not profitable.
As for the mineral resource, ok, yes but, again, the need investment and people to get them working again and the profits are questionable. That money would be much better placed elsewere in Ruzzia.
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Europe is in crisis in part because they are energy deprived. This after a dedicated and effective effort on multiple fronts to shoot themselves in the foot. Why? Who knows? Who cares? Seems like some mysterious group is dedicated to collapsing the West and it owns the political and media apparatus there-of and as such is getting them to happily commit suicide.
You know who isn't energy deprived? Yeah, that's right; Russia. When NATO has finally fought down to the last Ukrainian, much of Russia's apparatus to build multiple highly sophisticated and lethal ballistic missiles and a great many war-oriented other things will be released. Even after the fighting stops, Russia will probably be busy building weapons which have proven to win wars for other countries which want such a capability, but what is released could probably re-build Azovstal to ultra-modern standards in a matter of months. And again, the country has the energy resources to operate it. And now much of the previously 'Ukrainian' raw materials which used to supply it are within the Russian Federation's control.