Romanian authorities launch one of the most violent pogroms in Jewish history in the city of Iași, resulting in the murder of at least 13,266 Jews.

The Iai pogrom (Romanian pronunciation: [ja] (listen), sometimes anglicized as Jassy) was a series of pogroms launched by governmental forces under Marshal Ion Antonescu in the Romanian city of Iai against its Jewish community, which lasted from 29 June to 6 July 1941. According to Romanian authorities, over 13,266 people, or one third of the Jewish population, were massacred in the pogrom itself or in its aftermath, and many were deported. It was one of the worst pogroms during World War II.

Following the outbreak of World War II on 1 September 1939, the Kingdom of Romania under King Carol II officially adopted a position of neutrality. However, the rapidly changing situation in Europe during 1940, as well as domestic political upheaval, undermined this stance. Fascist political forces such as the Iron Guard rose in popularity and power, urging an alliance with Nazi Germany and its allies. As the military fortunes of Romania's two main guarantors of territorial integrity—France and Britain—crumbled in the Fall of France (May to June, 1940), the government of Romania turned to Germany in hopes of a similar guarantee, unaware that the then dominant European power had already granted its blessing to Soviet claims on Romanian territory in a secret protocol of 1939's Molotov–Ribbentrop Pact.

In the summer of 1940 diplomacy resolved a series of territorial disputes in a manner unfavorable to Romania, resulting in the loss of most of the territory gained in the wake of World War I. This caused the popularity of Romania's government to plummet, further reinforcing the fascist and military factions, who eventually staged a coup (September 1940) that turned the country into a dictatorship under Mareșal Ion Antonescu. The new regime firmly set the country on a course towards the Axis camp, officially joining the Axis powers on 23 November 1940. As a member of the Axis, Romania joined the invasion of the Soviet Union on 22 June 1941, providing equipment and oil to Nazi Germany as well as committing more troops to the Eastern Front than all the other allies of Germany combined. Romanian forces played a large role during fighting in Ukraine, Bessarabia, Stalingrad and elsewhere. Romanian troops were responsible for the persecution and massacre of 260,000 Jews in Romanian-controlled territories, though most Jews living within Romania survived the war. According to historian and author Mark Axworthy, the second Axis army in Europe, arguably, belonged to Romania, though some would dispute this, regarding the Italian army as more significant.As the tide of war turned against the Axis, the Allies bombed Romania from 1943 onwards, and advancing Soviet armies invaded the country in 1944. With popular support for Romania's participation in the war faltering and German-Romanian fronts collapsing under the Soviet onslaught, King Michael of Romania led a coup d'état that deposed the Antonescu regime (August 1944) and put Romania on the side of the Allies for the remainder of the war (Antonescu was executed in June 1946). Despite this late association with the winning side, Greater Romania was not restored. However, the country was able to regain Northern Transylvania from Hungary.