'Margarethe II' was the German unrealised contingency plan for the occupation of Romania in the event of that country’s collapse or defection (January/23 August 1944).
In the event, Romania later moved into the Soviet camp as a result of a statement by Soviet foreign minister Vyacheslav Molotov on 22 August 1944 that the USSR had sent forces into Romania for purely military reasons and desired neither Romanian subservience nor Romanian territory (though no mention was made of the return to Romania of the Bukovina and Bessarabia regions annexed on 26 June 1940).
The Germans seem to have been unaware of the conspiracy led by King Michael I to overthrow Maresal al România General Ion Antonescu, the Romanian 'Conducător', and to conclude an armistice with the Allies, and it came as a complete surprise when the king summoned Antonescu to the palace on 22 August and ordered him to come to an armistice with the Allies. Antonescu refused and was arrested, together with Germany’s ambassador and chief military liaison officer.
On 23 August, just as the Soviet forces were penetrating the Moldavian front, the king of Romania led a successful coup with support from opposition politicians and the army. At first considered to be not much more than a figurehead, Michael was able to depose the Antonescu dictatorship, and then offered a non-confrontational retreat to German ambassador Manfred von Killinger. But the Germans considered the king’s coup to be reversible and attempted to turn the situation back in their own favour by military force. The Romanian 1st Army, 2nd Army (forming), and what little was left of the 3rd and 4th Armies (one corps) were ordered by the king to defend Romania against any German attacks. The king offered to put the Romanian army, which at that time had something in the order of 1 million men, on the side of the Allies and, somewhat surprisingly given the fact that Soviet forces were already in occupation of parts of Romania, Iosif Stalin immediately recognised the king and the restoration of the Romanian monarchy.
This caused resulted in a Romanian split between those who still supported Germany and its armies and those who supported the new government, the latter often forming partisan groups and gradually gaining the more support. To the Germans the situation was very precarious as Romanian units had been integrated in the Axis defensive lines: not knowing which units were still loyal to the Axis cause and which ones joined the Soviets or discontinued fighting altogether, defensive lines could suddenly collapse.
In a radio broadcast on the night of 23 August, the king issued a ceasefire order, proclaimed Romania’s loyalty to the Allies, announced the acceptance of an armistice (to be signed on September 12) offered by the UK, USA and USSR, and declared war on Germany.
There was no time for the Germans to effect a full implementation of 'Margarethe II' as the Soviet forces of Marshal Sovetskogo Soyuza Rodion Ya. Malinovsky’s 2nd Ukrainian Front and General Fyedor I. Tolbukhin’s 3rd Ukrainian Front were about to fall on Generaloberst Johannes Friessner’s Heeresgruppe 'Südukraine' in northern Romania.
Adolf Hitler thus contented himself in the short term with ordering the German air units allocated to the defence of the Ploieşti oilfields to bomb Bucharest, with particular emphasis on the place and the prime minister’s residence. This was just what General Constantin Sănătescu, the new prime minister, needed as a pretext to declare war on Germany, which he did on 25 August.
The full folly of Hitler’s reaction was immediately seen on the battlefield, where General de armatâ Petre Dumitrescu’s Romanian 3rd Army was paired with General Maximilian Fretter-Pico’s 6th Army in the Armeegruppe 'Dumitrescu' and General de corp de armatâ Gheoghe Avramescu’s Romanian 4th Army with General Otto Wöhler’s 8th Army in the Armeegruppe 'Wöhler'. Of the 250-mile (400-km) front with the Soviets in Romania, the Romanians held about 100 miles (160 km), and they immediately downed arms, and seized the crossings over the Danube, Prut and Siretul rivers for use by the Soviets. The result was total disaster for Heeresgruppe 'Südukraine', which in little more than a fortnight lost virtually all of the 6th Army and part of the 8th Army, in all 16 out of 24 German divisions at a cost of some 105,000 men killed and 106,000 men taken prisoner.