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Hitler's Problem. Geographically the invasion of the Ukraine is now no more difficult for Germany than the invasion of Poland was a year ago. The Ukraine, like Poland, is almost entirely flat so that motorized columns can romp over it at will unless they meet their military match. The only major obstacles of terrain are the great rivers which flow southward into the Black Sea. While the Ukraine looks flat, it is actually underlaid by layers of rock sloping slightly upward to the east. These layers overlap one another like shingles and the rivers run beside the overlaps, with one low bank subject to flooding and one steep bluff on which most of the big towns lie. But the high bank in each case is on the west so that it presents no obstacle to an invasion from that direction. It offers an actual advantage, for when troops reach the bluff at any point their artillery can command the far bank and protect their crossing.
With Hungary largely under German domination Hitler might be able to launch an attack on the Ukraine from the new Hungarian frontier which lies in the passes of the Carpathians. From there his Army would have a downhill run to the plains. With a friendly totalitarian government in Rumania he might be able to launch his attack on the plains themselves.
Last summer the Russians annexed a piece of Rumania, thereby advancing their frontier from the Dniester to the Pruth River, thereby putting one more river barrier in front of an invader from this direction.
But from the part of Poland which they have acquired the Germans can march southeastward to outflank both these rivers. In fact it would be practical and might (Continued on third page following) be politically advantageous for them to undertake the entire invasion from this direction.
In the Balkans, Hitler would have a different military problem. No Balkan State has an army which could offer serious opposition to Mussolini or Stalin, much less Hitler. Two Balkan States, Hungary and Rumania, are already largely under Germany's thumb. But if Russia (already on excellent terms with Bulgaria) or some other power should take a hand in the Balkans, Hitler might have pressing reasons for intervening. Moreover, if Hitler is to pick up some of the French, Dutch and British possessions in the Far East his route in that direction leads through Istanbul and Bagdad. That also is his route to the oil fields of Mosul.
To reach Istanbul against opposition, a German Army, by any route it took, would have to fight its way through mountain passes. One set of passes leads through the mountains of Transylvania into the plain of the lower Danube, the route General von Falkenhayn took when he conquered Rumania in 1916. But the main route to Istanbul leads through Belgrade to Nish and thence through Sofia and down through the rich Bulgarian plain and the Maritsa Valley. From Nish through another pass is a route down the Vardar River to Salonika on the Aegean, a port which would serve as one terminus of an alternate route, by sea, through Suez to the East.
The mountains through which German Armies would have to pass on either of these excursions are excellent territory for guerrilla warfare. If a first-rate or even a second-rate army defended the passes, they might prove serious obstacles.