Until mid-March 1939, Germany had considered that "for military reasons a common Hungarian-Polish frontier was undesirable". Indeed, Hitler had warned Hungary not to touch the remainder of Slovakia when he authorized Hungary to occupy the rest of Carpathian Ruthenia in March 1939. He meant to use Slovakia as a staging ground for his planned invasion of Poland. In March 1939, Hitler changed his mind on the common Hungarian-Polish frontier and decided to betray Germany's ally, the Organization of Ukrainian Nationalists, who had already in 1938 begun organising Ukrainian military units in a "sich" outside Uzhhorod under German tutelage. Polish political and military authorities saw the "sich" as a danger to the neighbouring southeastern Poland, with its largely Ukrainian population. Hitler, however, was concerned that if a Ukrainian army that was organised in Rus accompanied German forces invading the Soviet Union, Ukrainian nationalists would insist on the establishment of an independent Ukraine. Hitler, who had plans for the natural and farming resources of Ukraine, did not want to have to deal with an independent Ukrainian government.