The Battle of Romania in World War II comprised several operations in or around Romania in 1944, as part of the Eastern Front, in which the Soviet Army defeated Axis forces in the area, Romania changed sides, and Soviet and Romanian forces drove the Germans back into Hungary. In the First Jassy–Kishinev Offensive, the Soviet Army attacked into Romania from the northeast, through the territory of present-day Moldova. Named after the two major cities Iași and Chișinău in the area, a series of military engagements took place between 8 April and 6 June 1944 with the objective of cutting off vital Axis defensive lines in Northern Romania, facilitating a subsequent advance by the Red Army into the entire Balkan region. Soviet forces failed to overcome German defenses in the region and the offensive operation ultimately failed, mainly due to the poor combat performance of Soviet troops and the effectiveness of German defensive preparations. The second major attack of the offensive, between 20 August and 29 August, was a Soviet victory. The German Sixth Army was encircled by the initial Soviet onslaught and was destroyed for the second time. On 23 August, King Michael of Romania led a coup d'état against Prime Minister Ion Antonescu; the new government surrendered to the Allies and declared war on Germany. Romanian historian Florin Constantiniu claims this shortened World War II in Europe by six months. The Axis front collapsed. In the north, the German Eighth Army retreated to Hungary with heavy losses. Elsewhere, many Germans were cut off and captured, such as the large security and anti-aircraft force posted at the Ploieștioil field. Other fragments of the German forces fled toward Hungary as best they could, fighting the Romanians and Soviet forces, which stormed through the Carpathian Mountains. The Soviet victory in Romania caused Bulgaria to withdraw from the Axis on 26 August, and allowed Soviet forces to invade it on 8 September. By 24 September, nearly all of Romania was under Allied control. Historian David Glantz asserts that the Soviets launched a First Jassy–Kishinev Offensive in this area between 8 April and 6 June. This attack failed.