About a mile from a border post that marks the last Ukrainian-controlled territory before Crimea, soldiers suddenly emerge from the long sea grass to check on an idling car.

Their concern over who comes and goes is no surprise. Should Russia decide to invade Ukraine as feared by the U.S., tanks and infantry would likely pour across this narrow causeway connecting the peninsula to the wide open steppe of southern Ukraine in numbers Europe hasn’t seen since 1945.

The strategic loss for Ukraine would be as huge as the prize would be for Russian President Vladimir Putin. A few miles up the road he could unblock a makeshift dam that has severed Crimea from its agricultural water supply since he annexed it in 2014. Moving east, he could connect the peninsula by land to Russia and those parts of Ukraine’s eastern Donbas region already controlled by Russian-armed separatists. By moving west to Odessa and its seaports, he could leave the remainder of Ukraine landlocked.