Logistics are the most vital part of any military campaign, and especially a proxy war like the one Russia is waging in Eastern Ukraine. There, under a variety of thin but effective guises, the Russians are supporting and supplying separatists who are fighting the Ukrainian government.

Yesterday, columns of armored vehicles crossed from Russia into Ukraine, flying separatist banners but with Russian troops seemingly along for the ride. This is a definite escalation—and one that hints at Russian president Vladimir Putin's next step: To step up support for the rebels, he needs a port.

Right now, separatists receive aid from Russia in two ways. One is by using the Izvaryne-Luhansk border crossing. This rail and road center is controlled by separatists, and is a focal point for either humanitarian aid or lethal support, depending upon whether you ask Russia or Ukraine, respectively. You can bet that the eyes and ears of the Ukrainians, and Western intelligence agencies, are fixed on this crossing. For instance, when U.S. national security advisor Susan Rice said on Twitter that Russia's incursions into Ukraine include "artillery, air (defense) systems, dozens of tanks and military personnel," the information is probably based on intelligence gleaned from a known border crossing.

Secondly, there are smuggling routes. The Russian-Ukrainian border is marked with dirt roads used by smugglers hauling gasoline loads from Russia.

But neither of these options are good for heavy armaments shipped in large quantities—especially if you don't want to be seen. For that type of support, you need a port. And in eastern Ukraine, that means the port city Mariupol. The armored column from Russia, which Ukraine says it repelled, was aimed for Mariupol.

The Ukrainian government still controls this city; steel workers organized and drove separatists from the Mariupol in June. But if the separatists were to gain control of this port, that would be a game changer. Under the guise of humanitarian aid, Russian could use huge ships to increase its support of the separatists, while at the same time become harder to observe. And every port is plugged into a regional hub of established transportation—vital in securing control of a region.

Last week the lights went out in Mariupol when the 220 kV Azovska substation shut down. More than 40 percent of the population in the city, and a lot of the outlying areas, has gone dark. The reason why is not immediately clear, but there is reason to believe that this move heralds the next battle for this strategic location.

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