They crossed the Soviet border on June 22, 1941, heading east. While the attacking spearheads made good progress, there were also difficulties from day one. Their generals weren't exactly surprised. Campaigning in this part of Europe has never been easy. The terrain was tough, the distances involved were vast, and logistics in this relatively underdeveloped land were nightmarish. And then there was the adversary: a Red Army that, while not particularly skilled or well trained, had enough manpower and modern equipment to cause any attacker some serious trouble in the field. The campaign started out in mobile mode, but soon bogged down into positional fighting that bled both sides and exhausted the invading army even as it was battering its way forward towards its strategic objectives. In the end, the Russian campaign would consume it altogether.
Ah yes, any student of the war might say: the Wehrmacht in Russia. Such a well known story. Dramatic early victories, sudden turnabout. Ultimate defeat.
The only problem is that I am talking about the Romanians.